Downloaded from

Transcription

1 Write the code number of the question paper on the TOP RIGHT CNER of your answer sheet. S. No. BLUE PRINT HALF YEARLY EXAMINATION CLASS XI PHYSICS THEY Marks Name Total 1 Units and Dimensions Vectors One Dim. Motion Two Dim. Motion Laws of Motion Work Energy Power Total 70

2 Write the code number of the question paper on the TOP RIGHT CNER of your answer sheet. HALF YEARLY EXAMINATION PHYICS (THEY) CLASS XI Code - B Time: 3 hr. Max. Marks: 70 General Instructions: (i) (ii) (iii) (iv) (v) (vi) The question paper carries 30 questions. Questions no. 1 to 8 are of 1 mark each. Question no. 9 to 18 are of 2 marks each. Question no. 19 to 27 are of 3 marks each. Question no. 28 to 30 are of 5 marks each. Any error in units, poorly drawn diagrams or missing diagrams will be penalized. 1. Is it possible for the velocity of an object to reverse direction while maintaining a constant acceleration? If so, give an example. 2. If a body is revolving in uniform circular motion, what is the direction of the net acceleration of the revolving body? 3. At what point on the trajectory of an oblique projectile is the velocity of projectile minimum? What is the value of velocity at that point? 4. What will be the effect of air resistance on the acceleration of freely falling objects? What is the acceleration with no air resistance? 5. In addition to the speedometer on the dashboard of every car is an odometer, which records the distance traveled. If the initial reading is set at zero at the beginning of a trip and the reading is 40 km one and half hour later, what has been your average speed? 6. A heavy cargo box falls off a plane flying horizontally in the direction of the arrow just when it was vertically above a car. Relative to the car, where will the cargo box crash land? 7. What is the magnitude of a unit vector? 8. For what angle between A and B, is A + B = B + A? 9. Prove the work energy theorem. 10. Let x and a stand for distance. Check the correctness of the equation: dd a 2 x = 1 2 a sss 1 a x

3 Write the code number of the question paper on the TOP RIGHT CNER of your answer sheet. 11. A constant force acts for 3 s on a mass of 16 kg and then ceases to act. During the next three seconds, the body covers 81 m, find the magnitude of the force if the body were initially at rest. 12. Suppose you roll off balls from a table top. Will the time taken by the ball to hit the floor depend on the horizontal speed of the ball? Explain your answer. 13. From the velocity- time plot shown in the figure, find the distance travelled by the particle during the first 40 seconds. Also, find the average velocity during this period. 14. The horizontal range of a projectile is 4 3 times its maximum height. Find the angle of projection. A ball is thrown horizontally from a point 100 m above the ground with a speed of 20m/s. Find (a) the time it takes to reach the ground (b) the horizontal distance it travels before reaching the ground. 15. A body travels a distance of 20 m in the 7 th second and 24m in the 9 th second. How much distance shall it travel in the 15 th second? 16. Find a vector whose magnitude is same as that of A = 12i 5j and whose direction is opposite (anti parallel) to that of B = 3i 4j. 17. Explain why is a punch more forceful with a bare fist than with a boxing glove? Define angle of friction. Prove the relation tanθ =µ. Where µ = coefficient of friction and θ= angle of friction. 18. In a hypothetical system of units, velocity (v), force (F) and time (T) are chosen as the fundamental units. Write the dimensions of mass in this system. 19. Prove that Newton s second law is the real law of motion. 20. If A = 3i 2j + 4k and B = - 5i + 2j k, then what is (A+B). (A 2B). 21. A pump on the ground floor of a building can pump up water to fill a tank of volume 30 m 3 in 15 min. If the tank is 40 m above the ground, and the efficiency of the pump is 30%, how much electric power is consumed by the pump? 22. Rajan lives in Delhi and works in Gurgaon 45 km away from his residence. The speed limit on the expressway is 75km/h but he is often late and drives at 85km/h to save time. With

4 Write the code number of the question paper on the TOP RIGHT CNER of your answer sheet. necessary calculations, find the time he saves by over- speeding on the expressway. Compare this time to 30 min. he will spend in getting a ticket when caught by the traffic police. On the basis of the results obtained, do you think over-speeding/traffic violations are really necessary? 23. A ball is thrown vertically upward with a speed of 28m/s. (a) Find the maximum height reached by the stone. (b)find the velocity of the stone one second before it reaches the maximum height. (c) Does the answer of part (b) change if the initial speed is more than 28m/s such as 40m/s or 80m/s. 24. A plane flying horizontally at 100 m/s at a height of 1000 m releases a bomb from it. Find (a) the time it takes to reach the ground (ii) the velocity with which it hits the target, (iii) the distance from the target when the bomb is dropped. (Take g = 10m/s 2 ) 25. The time of oscillation T of a small drop of liquid under surface tension depends upon the density (ρ), the radius r, and the surface tension S (defined as force per unit length). Derive dimensionally the relation for T. 26. A particle moving with a constant acceleration describes a distance of 8 cm in the third second of its motion and 9/25 th part of the whole distance in the last second of its motion. If the particle has started from rest, how long did it move and what distance? 27. The figure shows three blocks attached by mass-less cords that loop over frictionless pulleys. Block B lies on a frictionless table; the masses are m A = 6 Kg, m B = 8 Kg and m C = 10 kg. When the blocks are released, what is the tension in the cord at the right? 28. Define a projectile. For an oblique projectile derive an expression for the(i) equation of trajectory (ii) Time of flight (ii) Range. From the expression for range prove that the range is same for angle of projections θ and 90 - θ. A person is standing on a truck moving with a constant velocity of 14.7m/s on a horizontal road. The man throws a ball in such a way that it returns to the truck after the truck has moved 58.8 m. Find the speed and the angle of projection (a) as seen from the truck (b) as seen from the road.

5 Write the code number of the question paper on the TOP RIGHT CNER of your answer sheet. 29. Assuming perfectly elastic collision in one dimension, prove that if a truck of mass m 1 collides with a scooter of mass m 2 (m 2 <<m 1 ) at rest, the scooter will be thrown away with a velocity twice that of the initial velocity of the truck but there will hardly be any change in the velocity of truck. Two friends A and B (each weighing 40 kg) are sitting on a frictionless platform some distance d apart. A rolls a ball of mass 4 kg on the platform towards B which B catches and then B rolls the ball towards A and A catches it and rolls it back to A. The ball keeps on moving back and forth between A and B. The ball has a fixed speed of 5m/s on the platform. (a) Find the speed of A after he rolls the ball for the first time. (b) Find the speed of A after he receives the ball from B for the first time. (c) How many times can A roll the ball? 30. A car driver driving at the rate of 72km/hr sees a danger signal and applies the brakes. The brakes provide a retarding force, which is equal to ¾ of the weight of the car. Find the distance covered by the car after the driver sees the signal, if the reaction time (time interval between the appearance of signal and application of brakes) of the average driver is 0.7 sec. A bullet of mass 0.01 kg is fired horizontally into a 4 kg wooden block at rest on a horizontal surface. The co efficient of friction between the block and the surface is The bullet gets embedded in the block and the combination moves 20 m before coming to rest. What must be the speed of the bullet when it strikes the block?