3e purephy mye 06

Name : ______________________________________ ( ) Class: Sec 3E ___

BOWEN SECONDARY SCHOOL MID-YEAR EXAMINATION

17 May 2006 1 hour 30 minutes

Pure Physics

Secondary 3 Express

READ THESE INSTRUCTIONS FIRST

1. Answer all the questions in Section A on the OTAS sheet provided.

2. Answer all the questions in Section B and Section C in the space provided in the question paper.

3. The OTAS sheet for Section A and the answers for Section B and C should be handed up separately at the end of the examination.

4. The use of a suitable calculator is permitted.

5. The necessary workings should be shown clearly. Failure to do so may result in the loss of marks.

6. Where necessary, the value of the gravitational field strength may be taken to be 10N/kg.

This question paper consists of 22 printed pages.

E

Marks

Section A / 30

Section B / 40

Section C / 20

Total / 90

Section A : Multiple Choice Questions (30 marks)

Answer ALL the questions on the OTAS sheet provided.

1. What is the reading shown by the vernier caliper below ?

A. 0.50 cm B. 1.05 cm C. 1.95 cm D. 2.40 cm

2. What is the reading shown by the micrometer screw gauge below ?

A. 2.33 mm B. 2.83 mm C. 5.27 mm D. 5.33 mm

3. The diagram shows how a displacement can is used to measure the volume of an object. Which of the following is a necessary precaution to take to ensure the accuracy of the experiment ?

A. The object should be fully submerged in the water. B. The object must touch the bottom of the displacement can. C. The object should not touch the bottom of the displacement can. D. Only water should be used in the displacement can.

4. Which of the following actions will cause a pendulum to oscillate with a shorter period ?

A. The pendulum bob is changed to one with a greater mass. B. The pendulum bob is changed to one with a smaller mass. C. The length of the pendulum is increased. D. The length of the pendulum is decreased.

5. In an experiment to determine the periodic time of the pendulum, which of the following measurements is(are) necessary ?

I. The angle of the oscillation. II. The mass of the pendulum. III. The time taken for 1 oscillation only.IV. The time taken for 20 oscillations.

A. I and III B. II and III C. I , II and III D. IV only

6. A motorcycle was traveling at a speed of 24m/s when a group of young students began crossing the road a short distance ahead. The motorcycle immediately braked with a constant deceleration of 6m/s2. How much further did it move when the brakes were pressed until it came to a complete stop ?

A. 24m B. 48m C. 96m D. 144m

7. The graph shows how the velocity of a car changes with time.

Which of the following can be deduced from the graph?

A. The car starts from rest. B. The car accelerates uniformly in the beginning. C. The car stopped moving after t seconds. D. The car decelerates until it reaches a constant speed.

8. An object was tossed upwards and falls back down after a while. Which of the following graphs show how the velocity of the object varies with time ? Take the velocity in the upward direction as positive and ignore the effects of air resistance.

A. B. C. D.

velo

city

velo

city

velo

city

time

velo

city

time

time

time

velo

city

time

t

9 A car Y was just starting to move off at time t = 0s when another car X sped past it. The graph below shows the velocity-time time graphs of both cars X and Y over a period of 2 hours.

Which of the following statements is correct ?

A. Car X and car Y were traveling in opposite directions. B. Car Y overtook car X 1 hours after it started to move. C. Car Y overtook car X 1.5 hours after it started to move. D. Car Y overtook car X 2 hours after it started to move.

10. The diagram below shows the shape of a racetrack. MN and PQ are straight segments, while N-O-P and Q-R-M are semi-circular.

Suppose a race car traveled one complete round(M-N-O-P-Q-R, as indicated in the diagram) around the race track at a constant speed. Which of the following statements is correct ?

A. The velocity of the car from M to N is the same as that from P to Q. B. The acceleration of the car is changing only from N to O to P, and from Q to R to M. C. The velocity of the car is constant throughout. D. The acceleration of the car is zero throughout.

Car X Car Y

velo

cit

y

timeh

0 0.5 1 1.5 2

M N

R O

Q P

11. A trolley is pulled along by a stretched rubber band as shown in the diagram (i). The rubber band exerts a constant pulling force F on the trolley.

Diagram (i) Diagram (ii)

Suppose another identical trolley is now stacked on top of the first one, as shown is diagram (ii), and the experiment repeated. Ignoring the effects of friction, what is the effect of the second trolley on the resultant motion in diagram (ii) ?

A. The resultant acceleration is reduced by half compared to diagram (i). B. The resultant acceleration is doubled compared to diagram (i). C. The second trolley caused a resultant deceleration. D. The second trolley does not affect the motion because F is still the same.

12. Two bricks X and Y, of similar dimensions but made uniformly of different materials, are resting on a table. By giving each brick a gentle push as shown, it was found that brick X was more difficult to push aside than brick Y. Which of the following conclusions can be made from this simple experiment ?

A. Brick Y has more mass than brick X. B. Brick Y has a lower centre of gravity than brick X. C. Brick X has more mass than brick Y. D. Brick X has a lower centre of gravity than brick Y

13. After a parachutist had been falling for 10s, he reached terminal velocity. Which of the following statements is correct ?

A. The net acceleration of the parachutist was decreasing during the 10s. B. The net acceleration of the parachutist was constant during the 10s. C. The speed of the parachutist was decreasing during the 10s. D. The speed of the parachutist was constant during the 10s.

14. When an object is accelerating uniformly, which of the following quantities must be changing ?

A. velocity B. speed C. mass D. force

F F1st trolley 1st trolley

2nd trolley

X Y

push push

15. A pole is supported by two ropes as shown in the diagram. The tensions in the ropes are T1 = 200N and T2 = 120N.

Which of the following vector diagrams show correctly the tensions and the resultant force F exerted on the pole due to the ropes ?

A. B.

C. D.

16. Two forces F1 and F2 were acting on an object , causing it to move along a friction-less flat surface with an acceleration of 5m/s2 in the direction shown.

What is the mass of the object ?

A. B. C. D.

17. The density of an object is defined as its mass per unit volume. A gas has a lower density than a liquid and a solid because __________ .

A. the particles have a lower density B. the particles are bigger in size C. the particles have a lower mass D. all the particles occupy a larger volume than a liquid and a solid

F

T1 = 200N T2 = 120N

60 45

F

T1 = 200N T2 = 120N

60 45

F

T1 = 200NT2 = 120N

60

45

F

T1 = 200NT2 = 120N

6045

F2 – F1 5

F1F2direction of motion

F1 – F2 5

5 (F2 – F1)F1 5

pole

T1 = 200N T2 = 120N

60 45

18. An object has a weight of x N on the earth where the gravitational field strength is 10N/kg. Suppose the gravitational field strength on the moon is 1/6 that on the earth, what is the weight of the object on the moon ?

A. B. C. D.

19. The diagrams below shows a rock placed in different liquids X, Y and Z.


A. The rock has the same weight as liquid X. B. The rock is heavier than liquid Y. C. Liquid X is more dense than liquid Y. D. Liquid Y is more dense than liquid Z.

20. The diagram shows the weight of a motor car as well as other forces acting on it as it is accelerating along a road.

Which of the forces (A, B, C or D) is NOT shown correctly ?

21. The diagram shows two cubes M and N made from the same material. The lengths of each side of the cubes M and N are x and 2x respectively.


A. The mass of cube M the same as that of cube N. B. The mass of cube M is half that of cube N. C. The density of cube M the same as that of cube N. D. The density of cube M is half that of cube N.

x 2x

MN

16 x6x 10

6 x 6 x10

B. Air resistance

A. Reaction

C. Weight

D. Friction road

direction of motion

liquid X liquid Y liquid Z

22. The diagram shows a plastic lamina which is suspended freely from a point P1 near to its edge. The centre of gravity of the plastic lamina is marked “x” .

If the plastic lamina is now suspended freely from the point P2 and allowed to come to rest, which is of the following statements is correct ?

A. The plastic lamina will come to rest with “x” between P1 and P2. B. The plastic lamina will come to rest with “x” directly below P1. C. The plastic lamina will come to rest with “x” directly below P2. D. When the plastic lamina comes to rest, it will have a new centre of gravity.

23. The diagram shows a lever which is used to lift up an object of mass 20kg. What is the minimum force F required ? Assume that the weight of the lever is negligible and take the gravitational field strength to be 10N/kg.

A.

B.

C.

D.

24. The diagrams below show some plastic laminas of different shapes. Each of these objects are flat, are made of the same material, and have the same thickness and weight. Which one has the lowest centre of gravity ?

A. B. C. D.

20 x 10 x 0.350.78

20 x 10 x 0.40.9

20 x 0.350.78

20 x 0.40.9

P1

x

pin

P2

F

0.9m

0.4m

0.35m

0.78m

mass 20kg

lever

pivot

25. The diagrams below show laminas of various shapes. For which of the following would you expect the position of the centre of gravity to be outside the lamina ?

A. B. C. D.

26. Which quantity below has a unit equivalent to Joules per second ?

A. Work done B. Energy C. Efficiency D. Power

27. The diagram shows a pendulum which oscillates between the points X and Z.


A. The kinetic energy at X is greater than at Y. B. The kinetic energy at Y is greater than at Z. C. The kinetic energy at Z is maximum. D. The potential energy at Y is maximum.

28. An electric motor is used to lift a 500N load up to a height 3m. The total amount of electrical energy supplied to the motor is 2500J. What is the efficiency of the motor ?

A. 6.7% B. 20% C. 60% D. 167%

29. Which of the following show correctly the energy changes that take place when a battery operated torch light which uses a filament bulb is switched on?

A. electrical energy light energy B. electrical energy heat + light energy C. chemical energy electrical energy heat + light energy D. electrical energy chemical energy heat + light energy

ZY

X

30. An 10kg object was dropped from a height of 20m. Which of the following statements is correct for the duration when it is falling ? It may be assumed that the effects of air resistance is negligible.

A. Its loss in gravitational potential energy equals its gain in kinetic energy. B. Its gain in gravitational potential energy equals its gain in kinetic energy. C. Its loss in gravitational potential energy equals its total energy. D. Its loss in gravitational potential energy equals work done against air resistance.

End of Section A.

Section B [40 marks]Answer ALL the questions from this section in the space provided.

1. A flat circular disc called a puck, of mass 0.1kg, lies at rest on a flat horizontal surface. A steady force F, of magnitude 1.2N is applied to the puck for a time of 2.0s and then ceases to act. Suppose the frictional force between the puck and the surface during the motion is 0.2N.

a. Determine the acceleration of the puck while the force F is acting on it. [2]

b. Determine the speed of the puck at the end of 2.0s. [2]

c. Determine the deceleration of the puck after 2.0s. [2]

d. Draw, on the axes given below, the velocity-time graph for the motion of the puck, starting from the moment the force F is applied until it finally comes to rest again. [1]

2a. What is meant by “centre of gravity” of an object ? [1]

velocitym/s

times

0 1 2 3 4 5 6 7 8 9 10 11 12

25

20

15

10

5

0

b. The diagram below shows a uniform metre rule which is supported on a knife edge at the 50cm mark. Two objects, of mass 5kg and 8kg, are placed on the metre rule as shown. Take the gravitational field strength to be 10N/kg.

i. If the 5kg object is placed at the 10cm mark, determine where the 8kg object should be placed so that the metre rule is balanced horizontally ?

[2]

ii. Explain why the weight of the metre rule is not necessary in the calculation in part i. above. [2]

0cm 100cm

10cm

50cm

5kg 8kg

iii. Explain what will happen to the metre rule if the knife edge was now moved to the 60cm mark. [2]

3. The diagram below shows a roller-coaster ride. When the passengers have boarded the roller coaster at the ground level, a motor will hoist it up the first hill to point A. At point A, the roller-coaster was stationary for a short while before plunging freely towards points B and C.

Suppose the total mass of the roller-coaster and its passengers is 1200kg. and point A is 40m above the ground level.

a. What is the gain in gravitational potential energy of the roller-coaster and passengers at point A ? [2]

Point C

Point

B

Point A roller-coaster

tracks track

s

b. Would you expect the work done by the motor to be equal to, less than or greater than the gain in gravitational potential energy of the roller-coaster and passenger ? Explain your answer. [2]

c. Ignoring the effects of friction and air resistance, determine the velocity of the rollercoaster at point B. [2]

4. Refer to the diagram, which shows two objects of mass 5kg and 3kg, connected by an inextensible string over a frictionless wheel.

The 3kg object accelerates downwards at 2m/s2.

a. By considering only the 3kg object, calculate the tension in the string. [2]

a = 2m/s2

5kg

3kg

b. By using the appropriate Newton’s Law of Motion, determine the pulling force exerted by the string on the 5kg object. Explain your answer. [2]

c. By considering only the 5kg object, determine the frictional force between the 5kg object and the surface it is moving along. [2]

5. The diagram shows a rectangular block X with a mass of 600g.

a. Determine the density of the rectangular block X. [2]

8cm

20cm

10cmblock X

b. Consider another rectangular block Y with identical dimensions but of a higher density. Explain whether the rectangular block Y has a greater or smaller mass than X. [2]

6. The diagrams A and B show two experiments which were carried out on the object labeled X on earth.

a. State what quantity is being measured in each case. [2]

b. State the changes, if any, to the results in each case if the experiments were carried out on the Moon, where the gravitational field strength is less than that of the earth’s. [2]

7a. What is the difference between a scalar quantity and a vector quantity ? [1]

b. Two men were trying to move a heavy heater box by each trying a rope around it and pulling it horizontally.

One man pulled with a force of 300N while the other pulled with a force of 200N. The directions of the forces can be seen from the top view as shown in the diagram.

i. Draw a suitably scaled diagram in the box below that shows the resultant force. State the scale used in the drawing. [3]

Scale : ………………………………………………..

60

200N

300N

box

ii. Determine the magnitude of the resultant force. [1]

iii. State whether the angle between the two pulling forces should be larger or smaller in order to obtain a larger resultant force. [1]

End of Section B

Section C [20 marks]Answer ALL the questions from this section in the space provided.

1. The diagrams below shows a balancing toy. It consists of a plastic figurine of a weight-lifter which is balanced on a vertical stand. The two identical balls that represent the weights which the weight-lifter is carrying is made of metal. Diagram (i) shows the toy when it is perfectly balanced.

a. i. Indicate on the diagram (i), using the letter X, a probable position of the centre of gravity of the figurine. [1]

ii. State how your answer will be different if the plastic figurine was also made of metal instead. [1]

b. The toy was then tilted about the pivot until the position shown in diagram (ii). Indicate, again, on the diagram (ii), using the letter X, the centre of gravity of the toy. [1]

d. Suppose the total weight of the figurine and the two circular weights is W. Indicate the weight W on diagram(ii) and use it to explain whether the toy will topple over. [4]

vertical stand

plastic figurine

metallic weights

Diagram (i) Diagram (ii)

d. By considering only the weights of the two identical balls, explain how this toy verifies the Principle of Moments when it is balanced. [3]

2. A car of was moving at 20m/s when it collided into a lamp-post. The seat belt which the driver was wearing was stretched and caused the driver to spring forward by 40cm (see diagram) before stopping the driver from hitting the windscreen.

The mass of the car is 1200kg. The mass of the driver is 80kg.

a. Explain, using Newton's law, why the driver would be "thrown forward" and hit the windscreen if he was not wearing the seat belt. [2]

b. i. Calculate the kinetic energy of the driver just before the collision . [2]

ii. Use your answer above in b(i) to determine the average retarding force which was exerted by the seat belt on the driver? [2]

40cm

driver

seat belt

c. In the collision, the front part of the car, called the crumple zone, was crushed by the impact. The crumple zone reduced the abruptness of the sudden halt to the car’s motion and cushioned some of the collision force. When the crumple zone was crushed, the car finally came to a complete stop in 0.05s.

i. Calculate the deceleration of the car. [2]

ii. Calculate the force of collision on the car. [2]

End of Section C.

Bowen Secondary School Mid Year Examination 2006Sec Three Express : Pure Physics

Answers

Section A

1.

C 6.

B 11.

A 16.

B 21.

C 26.

D

2.

B 7.

B 12.

C 17.

D 22.

C 27.

B

3.

A 8.

C 13.

A 18.

B 23.

C 28.

C

4.

D 9.

D 14.

A 19.

C 24.

B 29.

C

5.

D 10.

B 15.

B 20.

D 25.

C 30.

A

Section B [40 marks]

1a. b.

[2]

[2]

c.

[2]

d. [1]

velocitym/s

times

0 1 2 3 4 5 6 7 8 9 10 11 12

25

20

15

10

5

0

2a. …. the position where the whole weight of the object seem to act. [1]

b. i. Let the 8kg object be place at a distance , d , to the right of the pivot. By Principle of Moment, taking moments about 50cm mark,

(5kg x 10N/kg) x 0.4m = (8kg x 10N/kg) x d

hence, d = 20Nm 80N

= 0.25m [2]

[ Allow the answer d = 0.25m if d is explicitly stated. Else, the answer is 70cm. ]

ii. … line of action of the weight of the ruler passes through the pivot [1] … hence, the weight does not produce any moment about the pivot [1]

iii. … anti-clockwise moment will be greater than clockwise moment [1] … hence, the ruler will turn in the direction of the anticlockwise moment [1]

3a. Gain in PE = 1200kg x 10N/kg x 40m = 480 000J [2]

b. … work done by motor expected to be greater than gain in PE [1] … reason : energy loss due to work done against friction, heat, sound [1]

c.

[2]

4a. Weight - Tension = m x a (3kg x 10N/kg) - T = 3kg x 2m/s2

T = 30N - 6N = 24N [2]

b. Pulling force on 5kg object = tension in string = 24N [1] According to Newton’s 3rd Law, force exerted by 3kg on 5kg object = force exerted by 5kg on 3kg object

= 24N [1]

c. Net force on 5kg object = m x a 24N - Friction = 5kg x 2m/s2

Friction = 24N - 10N = 14N [2]

5a.

[2]

b. … Y has a greater mass [1] … mass = density x volume , hence, higher density implies greater mass if volume is fixed [1]

6a. Diagram A : measuring mass [1] Diagram B : measuring weight [1]

b. Mass remains unchanged. [1] Weight is lesser. [1]

7a. A vector quantity has a direction; a scalar does not have a direction. [1]

b. i. Correct vector diagram [3] subject to following penalty [-1] ….. Scale should not be less than 1 cm : 50N [-1] ….. accuracy of measurements in the diagram

ii. Resultant force = measured length x scale = 435.9N 10N

Acceptable range : 425.9 < resultant < 445.9N

iii. To obtain a larger resultant force, the angle should be smaller. [1]

End of Section B.

[1]

Section C [20 marks]

1a. i.

b. The C.G is in the same position, relative to the toy, as indicated on above. [1]

c. Draw on diagram (ii) a downward arrow at the C.G. [1]

... the weight produce a clockwise moment [1] ... which returns the toy back towards its upright position [1] ... hence, the toy will not topple. [1]

d. ... both balls are identical in weight and distance away from pivot, their moments are equal in magnitude. [1] ... one metal ball produce clockwise moment, the other anti-clockwise [1] ... therefore, when toy is balanced, clockwise moment = anti-clockwise moment [1]

2a. ... according to Newton’s 1st Law ; [1] ... driver continues to move forward with speed because of inertia [1]

b. i. before collision, KE = ½ x 80kg x ( 20 m/s x 20 m/s) = 16 000J [2]

ii. Work done by seat belt = Loss in KE of driver F x 0.4m = 16 000 J ------ [1] retarding force, F = ( 16 000 0.4 )

= 40 000N ------ [1]

c. i. Deceleration = ( 20 m/s 0.05s ) = 400 m/s2 [2]

X [1]

ii. If the figurine is also made of metal, the C.G. will be higher. [1]

ii. Collision force , F = 1200 kg x 400 m/s2

= 480 000N [2]

End of Section C.

3e purephy mye 06

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