force and motion
TRANSCRIPT
Chapter 5 Force and Motion Date: ________________
Section A: Multiple Choice Questions
1 If there is no reaction force, which of the following cases will occur?
(1) We cannot swim.
(2) We cannot jump.
(3) We cannot walk.
A. (1) only B. (2) only
C. (3) only D. (1), (2) and (3)
2 A lift and three men inside have a total mass of 600 kg. If the lift is accelerating upwards with
acceleration of 1.1 m s−2, find the tension in the cable of the lift.
A. 1 560 N B. 4 830 N
C. 5 060 N D. 6 660 N
3 A parachutist opens a parachute and an upward force is acting on it. The parachutist and parachute
is still accelerating downwards with 1 m s−2. Find the force of air friction given that the mass of the
parachutist and parachute is 50 kg and 5 kg respectively.
A. 495 N B. 480 N
C. 470 N D. 505 N
4 An astronaut or a car-racing driver should be able to resist great force because of the extremely
great acceleration and deceleration. For example in a rocket racing car match in 1954, the driver
decelerated from 1 000 km h−1 to rest in just 1.4 s. Try to estimate the magnitude of the force acting
on a 50 kg driver?
A. 8 920 N B. 9 920 N
C. 10 020 N D. 7 920 N
5 The figure below shows a grab handle inside a moving train. The train is moving towards left. Which
of the statements is CORRECT?
A. The train is accelerating.
B. The train is decelerating.
C. The train is moving with a constant speed.
D. The status of motion cannot be determined from the figure.
6 The flag is now in equilibrium as shown in the figure. Calculate the value of tension T.
A. 6.88 N
B. 9.2 N
C. 2.37 N
D. 4.73 N
Force_and_Motion.doc
7 A man uses a pulley system to slow down the falling of a box. Find the acceleration of the box.
Given that the mass of the box is 7 kg and the weight is 5 kg and the string is inextensible.
A. 2.87 N downwards
B. 1.50 N upwards
C. 1.67 N downwards
D. 2.02 N upwards
8 As shown in the figure, a cart is at rest on a frictionless surface. If the fan is turned on, which of the
following is/are the CORRECT description?
(1) The cart will not move.
(2) The cart will move.
(3) The cart will move to and fro on
the frictionless surface.
A. (1) only B. (2) only C. (3) only D. None of the above
9 If a parachutist falls freely from an aircraft, which of the following quantities are kept constant?
(Assume that air friction is negligible and g is independent of the height from the earth.)
A. Mass only.
B. Mass and weight.
C. Mass, weight and acceleration.
D. Mass, weight, velocity and acceleration.
10 Which of the following statements is / are CORRECT?
(1) The weight of a man on the Moon is smaller than that on the Earth.
(2) The mass of a man is the same on both the Moon and the Earth.
(3) We cannot determine our own mass in the outer space because there is no gravity.
A. (1) only
B. (3) only
C. (2) and (3) only
D. (1) and (2) only
11 As shown in the figure, two forces of 10 N and 17 N are now acting on a point mass A. In order to
keep A in equilibrium, what should be the magnitude of the third horizontal force needed to be
added?
A. 24 N
B. 27 N
C. 18 N
D. 13 N
Force_and_Motion.doc
12 Calculate the horizontal component of the resultant force exerted on the ball.
A. 9.28 N to the right
B. 0.62 N to the right
C. 0.62 N to the left
D. 2 N to the right
13 A pendulum bob is hung on a fixed end and is pulled aside to a height h. If a peg is put within the
path of the bead as shown in the figure, which of the following figures correctly describe the motion
of the bead?
A. B.
C. D.
14 Which of the following free body diagram represents the point particle is in equilibrium?
(1)
(2)
(3)
A. (1) only B. (2) only
C. (3) only D. (1), (2) and (3)
Force_and_Motion.doc
15 In the Galileo’s thought experiment, a ball bearing is allowed to roll on a curtain rail of different
curvatures as shown in the figure. What physics concept is demonstrated in this experiment?
A. Inertia of the ball bearing.
B. Gravitational force acting on the ball bearing. C. Action and reaction pair on the ball bearing and on the rail.
D. The weight of the bead.
16 Which of the following statements is / are CORRECT?
(1) The angle of friction-compensated inclined plane will be different for different objects put on
the plane.
(2) The magnitude of friction depends on the material of the surface.
(3) Friction does not exist if there is no relative motion between two surfaces.
A. (1) only B. (1) and (2) only
C. (2) and (3) only D. (1), (2) and (3)
17 Which of the following cases is / are the CORRECT explanation concerning a point mass, which is
accelerating on a friction compensated inclined plane.
(1) There is an unbalanced force acting on the point mass.
(2) The phenomenon can explain by the Newton’s second law.
(3) The unbalanced force which cause the acceleration is the gravitational force.
(4) The unbalanced force which cause the acceleration is the frictional force.
A. (1) and (2) only B. (2) and (3) only
C. (3) and (4) only D. (2), (3) and (4) only
18 Two blocks are connected by a string, and are pulled by a force of 5.7 N on a frictionless surface as
shown in the figure. If the string breaks suddenly, calculate the acceleration of the heavier block
along the plane.
A. 0.87 m s−2
B. 2.60 m s−2
C. 8.66 m s−2
D. 5.00 m s−2
Force_and_Motion.doc
19 In the following figure, calculate the value of force exerted on the 1.5 kg block by the 2.5 kg block.
Given that all surfaces are frictionless.
A. 25.0 N
B. 28.2 N
C. 27.6 N
D. 19.4 N
20 Calculate the value of the air friction if a 1.2 kg ball is dropped under the action of gravity but moving
at a uniform speed.
A. 20 N B. 12 N
C. 30 N D. 16 N Section B: Questions
1 The figure shows a man pulling an ice block of 100 kg.
(a) If the friction between the ground and the ice is 150 N, find the force needed to pull
the ice with a uniform speed.
Ans:
(b) Suggest a method to reduce the magnitude of the applied force.
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(c) “Although it is hard to pull the ice initially, but it is easier to pull it at a latter time.”
Comment on this statement and explain briefly.
Ans:
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2 The following figure shows a frictionless inclined plane with angle θ. A mass of 2 kg is projected up
with an initial speed of 0.6 m s–1.
(a) If θ equals to 45°, find the vertical height reached by the mass.
Ans:
(b) If θ equals to 30°, find the vertical height reached by the mass.
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(c) According to the result in (a) and (b), state the relation between the inclined angle θ and
the vertical height reached by the mass.
Ans:
Force_and_Motion.doc
3 An aircraft of 7 500 kg is flying up the sky as shown in the figure. It is known that there is a thrust (T)
directing the aircraft forward, and an uplift force (L) perpendicular to the wings of the aircraft.
(a) Draw a free body diagram to show ALL the forces acting on the aircraft.
Ans:
(b) If the acceleration of the aircraft is 10 m s-2, find the value of
(i) thrust (T),
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(ii) uplift force (L).
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(c) If the magnitude of the acceleration is not given, can we calculate the value of thrust
and uplift force?
Ans:
End
Force_and_Motion.doc