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#### Nature of Physical World and Measurement - 3 marks

11th Standard

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Physics

Time : 01:30:00 Hrs
Total Marks : 100
Part-A
33 x 3 = 99
1. Suppose that the earth revolves around the sun in a perfectly circular orbit. Does the sun do any work on the earth?

2. A body is displaced 10 $\hat{j}$  under the force of $-2\hat{j}+15\hat{j}+6\hat{i}\ N.$ Calculate the work done.

3. In some demonstration, a police officer fires a bullet of mass 50.0g with speed 200 ms-1 on soft plywood of thickness 2.00 cm. The bullet emerges with only 10% of its initial kinetic energy. What is the emergent speed of the bullet?

4. A body of mass 5 kg initially at rest is subjected to a force of 20N: What is the kinetic energy acquired by the body at the end of 10s?

5. A ball of mass m is pushed down the wall of hemispherical bowl from point A.. It just rises up to edge Q of the bowl. Find the speed at which baU is pushed down.

6. A body of mass 0.3 kg is taken up an inclined plane of length 10 m and height 5 m and then allowed to slide down to bottom again. Find
(i) work done by frictional force over the round trip if $\mu$ = 0.15.
(ii) kinetic energy at the end of the trip.

7. A ball of mass0.1 kg collides elastically with a ban of unknown mass at rest. If 0.1 kg ball rebounds at 1/3 of the original speed, find the mass of other ball.

8. Calculate work done from the graph.

9. What is the stopping distance for a vehicle, of mass m moving with speed v along a level road, if the co-efficient of friction between the tyres and the road is $\mu$?

10. A partic e moves along the x-axis from x = 0 to x = 5m under the influence of a force given by F = 7 - 2x + 3x2.Find the work done in the process.

11. Calculate the velocity of the bob of a simple pendulum at its mean position if it is able to rise to a vertical height of 10 cm. Take g = 9.8 m/s2.

12. The potential energy of a spring when stretched through a distance x is 10J. What is the amount of work done on the same spring to sketch it through an additional distance 'x'?

13. One coolie takes 1 min to raise a box through a height 2m. Another takes 30 m/s for the same job and does the same amount of work. Which one of these two has a greater power?

14. After perfectly inelastic collision between two identical particles moving with same speed in different directions, the speed of the particles become half the initial speed. Find the angle between the two before collision.

15. What is meant by perfectly inelastic collision?

16. What do you mean by "Perfect elastic"?

17. A weight lifter lifts a mass of 250 kg with a force 5000 N to the height of 5m
(a) What is the work done by the weight lifter?
(b) What is the work done by the gravity?
(c) What is the net work done on the object?

18. How much work is done by a coolie walking on a horizontal platform with a load on his head? Explain.

19. Mountain roads rarely go straight up the slope, but wind up gradually. Why?

20. A truck and a car moving with the same K.E. on a straight road. Their engines are simultaneously switched off which one will stop at a lesser distance?

21. Is it necessary that work done in the motion of a body over a closed loop is zero for every force in nature? Why?

22. How high must a body be lifted to gain an amount of P.E.· equal to the K.E. it has when moving at speed 20 ms-1. (The value of acceleration due to gravity at a place is 9.8 ms-2).

23. Give an example in which a force does work on a body but fails to change its K.E.

24. Two objects of masses 2 kg and 4 kg are moving with the same momentum of 20 kg m s-1
(a) Will they have same kinetic energy?
(b) Will they have same speed?

25. An object of mass 2 kg is taken to a height 5 m from the ground (g = 10 ms-2 ).
(a) Calculate the potential energy stored in the object.
(b) Where does this potential energy come from?
(c) What external force must act to bring the mass to that height?
(d) What is the net force that acts on the object while the object is taken to the height 'h'?

26. Let the two springs A and B be such that kA > kB, On which spring will more work has to be done if they are stretched by the same force?

27. A body of mass m is attached to the spring which is elongated to 25 cm by an applied force from its equilibrium position.
(a) Calculate the potential energy stored in the spring-mass system?
(b) What is the work done by the spring force in this elongation?
(c) Suppose the spring is compressed to the same 25 cm, calculate the potential energy stored and also the work done by the spring force during compression. (The spring constant, k= 0.1 N m-1).

28. Compute the work done by the gravitational force for the following cases

29. Consider an object of mass 2 kg moved by an external force 20 N in a surface having coefficient of kinetic friction 0.9 to a distance 10 m. What is the work done by the external force and kinetic friction? Comment on the result. (Assume g = 10 ms-2)

30. A body of mass 100 kg is lifted to a height 10 m from the ground in two different ways as shown in the figure. What is the work done by the gravity in both the cases? Why is it easier to take the object through a ramp?

31. An object of mass 2 kg attached to a spring is moved to a distance x = 10 m from its equilibrium position. The spring constant k = 1N m-1 and assume that the surface is frictionless.
(a) When the mass crosses the equilibrium position, what is the speed of the mass?
(b) What is the force that acts on the object when the mass crosses the equilibrium position and extreme position x = ± 10m?

32. A vehicle of mass 1250 kg is driven with an acceleration 0.2 along a straight level road against an external resistive force 500 N. Calculate the power delivered by the vehicle's engine if the velocity of the vehicle is 30 ms-1.

33. A lighter particle moving with a speed of 10 ms-1 collides with an object of double its mass moving in the same direction with half its speed. Assume that the collision is a one dimensional elastic collision. What will be the speed of both particles after the collision?