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Academic Session: 2013-14

First Term Examination Subject : Physics

Class-XI Set 1

TIME : 3 Hrs. M.M. 70

GENERAL INSTRUCTIONS:

All questions are compulsory.

Question number 1 to 5 are very short answer questions, carrying one mark each.

Question number 6 to 10 are short answer questions, carrying two marks each.

Question number 11 to 22 are short answer questions, carrying three marks each.

Question number 23 is a value based question , carrying four marks .

Question number 24 to 26 are long answer questions, carrying five marks each.

This paper has 4 printed pages.

1 A projectile is fired at an angle of 300 with the horizontal. At what angle with the vertical does the projectile hit the ground in the same level as the point of projection?

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2 Which of the following is the most precise device for measuring length : (a) a vernier calipers with 20 divisions on the sliding scale coinciding with 19 divisions on the main scale , each main scale division being 1mm in length. (b) A screw gauge of pitch 2mm and 100 divisions on the circular scale.

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3 Why does a cricket player lower his hands to catch the ball safely ? 1

4 When the horse suddenly stops, the rider falls forward. Explain why.

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5 A ball is thrown straight up. What is its velocity and acceleration at the top?

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6 A projectile can have the same range R for two angles of projection, when projected with the same velocity. If t1 and t2 be the time of flight in the two cases, then prove that t1t2 = 2R/g.

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7 An elevator is ascending with uniform acceleration. To measure the acceleration of the elevator, a person in it drops a coin from a height of 1m above the floor of the elevator. The coin strikes the floor in 0.4 s. Find the acceleration of the elevator.

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8 A stone dropped from the window of a stationary railway carriage takes 1 second to reach the ground. In what time the stone will reach the ground when the carriage is moving with a) a constant velocity of 50 Km/h b) constant acceleration of 20km/h2 ?

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9 If heat dissipated in a resistance can be determined from the relation: H = I2Rt joule , if the maximum error in the measurement of current , resistance and time are 2% ,1% ,

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SANSKRITI SCHOOL

Dr S Radhakrishnan Marg

New Delhi

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and 2% respectively, what would be the maximum error in the dissipated heat?

10 The density of material in CGS system is 8g/cc. In a system in which unit of length is 5 cm and unit of mass is 20g, what is the density of the material? OR Two students were asked to write the displacement y of a particle having periodic motion. They wrote the expressions respectively as given below. (i) y = A sin(ωt) (ii) y = A sin(vt) Where A is maximum distance of particle from its mean position, ω is the angular velocity, t is time, and v is the velocity of particle. Explain which of these expressions is correct?

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11 Using dimensional analysis determine an expression for the velocity of sound ‘v’ in a gaseous medium if it is found to depend on pressure ‘P’ of the gas , density ‘d ‘of the medium and time ‘t’.

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12 A body is dropped from rest at a height of 150 m and simultaneously another body is dropped from rest from a point 100m above the ground. What is their difference in height after they have fallen for (i) 1s (ii) 2s ? How does the difference in height vary with time?

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13 The motion of a car along y axis is given by the relation y= t3– 6t2+9t+5, where y is in meter and t is in second. Calculate the velocity and acceleration , both at t=3 seconds. Draw the corresponding acceleration-time graph.

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14 Two cars A and B are at positions 100 m and 200 m from the origin at time t=0. They start simultaneously with velocities 10 m/s and 5 m/s respectively. At what position from the origin will the car A overtake the car B ?

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15 Two vectors A and B are inclined to each other at an angle θ. Using parallelogram law of vector addition, find the magnitude and direction of their resultant.

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16 Rain is falling vertically with a speed of 30ms-1. A woman rides a bicycle with a speed of 10ms-1 in the north to south direction. What is the relative velocity of rain with respect to the woman? What is the direction in which she should hold her umbrella to protect herself from the rain?

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17 Define Dot product of two vectors.

Find the value of λ so that the vectors ⃗ = 2i + λj + k and ⃗⃗ = 4i – 2j – 2k are perpendicular to each other.

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18 The length of a rod measured in an experiment was found to be 2.48m, 2.46, 2.50m and 2.48m and 2.49m. Find the mean absolute error and percentage error.

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19 Explain the triangulation method for finding the height of an inaccessible object. 3

20 State Newton’s second law of motion. A constant force acts on a body. Draw its force- time graph. Name the physical quantity given by area under F-t graph. Write its SI unit.

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OR Define limiting friction. Draw a labeled graph showing the variation of frictional force with the applied force. State two methods used to reduce friction.

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21 A monkey of mass 40 kg climbs on a rope which can stand a maximum tension of 600 N . In which of the following cases will the rope break and why? The monkey :

(a) climbs up with a acceleration of 6 m/s2 (b) climbs down with an acceleration of 4m/s2 (c) climbs up with a uniform speed of 5 m/s Take g =10 m/s2 and neglect the mass of the rope.

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22 Three blocks are connected as shown in the figure on a horizontal frictionless table and pulled to the left with a force of 50N. Find the tensions in the strings between A & B, and between B & C.

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23 Suresh noticed a big Granite Rock in his locality blocking the road. He thought that if they worked upon it they could help the locality and also earn money. He took permission from the Government, completed all the formalities .He broke the Rock using a bomb. The rock was made into slices and sold . Many of the people in the surroundings earned some money and started to travel comfortably. (a) What values of Suresh impress you? Mention any two values. (b) A bomb is thrown in a horizontal direction with a velocity of 50 m/s. It explodes into two parts of masses 6 Kg and 3 Kg. The heavier fragment continues to move in the horizontal direction with a velocity of 80 m/s . Calculate the velocity of the lighter fragment.

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24 Define angle of friction and angle of repose. Hence show that angle of friction is equal to the angle of repose. The force required to just move a body up an inclined plane is double the force required to prevent the body from sliding down. Find the coefficient of friction. OR Why does a cyclist lean inwards while moving along a curved path? Determine the angle from the vertical , through which he bends while negotiating the curve. A cyclist speeding at 18 km/h on a level road takes a sharp turn of radius 3m without reducing the speed and without bending towards the centre of the circular path. The coefficient of static friction between the tyres and the road is 0.1 . Will the cyclist slip while talking the turn?

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25 Derive an equation for the distance travelled by a uniformly accelerated body in the nth second of its motion. Draw and discuss the position-time graphs of two objects moving along a straight line, when their relative velocity is (i) zero (ii) positive and (iii) negative. OR From the velocity-time graph of uniformly accelerated motion in one dimension, deduce the third equation of motion in distance and velocity. A person goes to the post-office with a constant speed and purchases post-cards for some time . He then comes back with a constant speed. Draw the position-time and velocity- time graphs for the person.

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26 Define centripetal acceleration. Derive an expression for the centripetal acceleration of a particle moving with constant speed v along a circular path of radius r. A body is moving with a uniform speed in a circular path of radius R. If n is the frequency of circular motion , then what will be the centripetal acceleration in terms of n and R ? OR A projectile is projected horizontally with velocity u from height h above the ground. Find the expression of time of flight , horizontal range and velocity of projectile with which it strikes the ground. Prove that its path is parabolic.

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