#### Important 3mark -chapter 3,4

11th Standard

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Physics

Use blue pen Only

Time : 01:00:00 Hrs
Total Marks : 120

Part A

40 x 3 = 120
1. Under what condition will a car skid on a leveled circular road?

2. Can the coefficient of friction be more than one?

3. Can we predict the direction of motion of a body from the direction of force on it?

4. A body of mass 1.5 kg rest an a horizontal plane, and the angle of friction is 45°. Find the least force required to move the body along the plane

5. What are the steps which have to be followed before applying Newton's laws?

6. A cyclist starts from rest with moving down a hill with constant acceleration at a distance of 100 m in 30 s.
(i) Find acceleration and
(ii) Find the force acting on it if its mass is 100 kilograms.

7. A constant force acting on a body of mass 7 kg changes its speed from 3.0 msin-1  40 s. The direction of the motion of the body remains unchanged. What Js the magnitude and direction of the force?

8. A person of mass 75 kg stands on a weighing scale on a lift. If the lift is descending with a downwards acceleration of 5 ms-2, what would be the reading of the weighing scale?

9. For the following situation, Explain with an example.

10. Explain the meaning of law of conservation of linear momentum.

11. Draw and explain the variations of force of friction vs applied force graphically.

12. With an activity prove that coefficient of static friction varies from object to object.

13. The initial speed of a body of mass 2.0 kg is 5.0 ms-1. A force act for 4s in the direction of motion of the body. The force-time graph is shown in the diagram. Calculate the impulse of the force and the final speed of the body.

14. The position vector of a particle is given by $\vec { r } =3t\hat { i } +5t^{ 2 }\hat { j } +7\hat { k }$. Find the direction in which the particle experiences net force?

15. Consider a horse attached to the cart which is initially at rest. If the horse starts walking forward, the cart also accelerates in the forward direction. If the horse pulls the cart with force Fh in forward direction, then according to Newton's third law, the cart also pulls the horse by equivalent opposite force Fc = Fh in backward direction. Then total force on 'cart+horse' is zero. Why is it then the 'cart+horse' accelerates and moves forward?

16. A man getting out of a moving bus runs in the same direction for a certain distance. Comment.

17. A force of 36 dynes is inclined to the horizontal at an angle of 60°. Find the acceleration in a mass of 18 g that moves in a horizontal direction.

18. A spring balance is attached to the ceiling of a lift. When the lift is at rest spring balance reads 49 N of a body hang on it. If the lift moves:
(i) Downward
(ii) upward, with an acceleration of 5 ms-2
(iii) with a constant velocity.
What will be the reading of the balance in each case?

19. A block of mass 500 g is at rest on a horizontal table. What steady force is required to give the block a velocity of 200 cms-1 in 4 s?

20. A force of 98 N is just required to move a mass of 45 kg on a rough horizontal surface. Find the coefficient of friction and angle of friction?

21. What is meant by negative work? Give example.

22. What is mechanical energy? What are its two types?

23. What does the work-kinetic energy theorem imply?

24. What is conservative force? State how it is determined from potential energy?

25. Define the following
a) Coefficient of restitution
b) Power
c) Law of conservation of energy
d) loss of kinetic energy in inelastic collision

26. A spring which is initially in un-stretched condition, is first stretched by a length x and again by a further length x. The work done in the first case W1 is one third of the work done in second case W2True or false?

27. Which is conserved in inelastic collision? Total energy (or) Kinetic energy?

28. 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.

29. 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?

30. 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.

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

32. 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?

33. A ball at rest is dropped from a height of 12 m. It loses 25% of its kinetic energy in striking the ground, find the height to which it bounces. How do you account for the loss in kinetic energy?

34. A spring of force constant K is cut into two equal pieces. Calculate force constant of each part.

35. An elevator which can carry a maximum load of 1800 kg (elevator + passengers) is moving up at a constant speed of 2 ms-1. The frictional force opposing the motion is 4000 N. Determine the minimum power delivered by the motor to the elevator in watts as well as in horsepower.

36. To simulate car accidents, auto manufacturers study the collisions of moving cars with mounted springs of different spring constants. Consider a typical simulation with a car of mass 1000 kg moving with a speed 18.0 krnh-1 on a smooth road and colliding with a horizontally mounted spring of spring constant 6.25 x 10-3 Nm-1. What is the maximum compression of the spring?

37. A particle moves along X- axis from x = 0 to x = 8 under the influence of a force given by F = 3x2 - 4x + 5. Find the work done in the process.

38. A body of mass 10 kg at rest is subjected to a force of 16N. Find the kinetic energy at the end of 10 s.

39. A particle of mass m is fixed to one end of a light spring of force constant k and unstretched length I. It is rotated with an angular velocity w in horizontal circle. What will be the length increase in the spring?

40. 20 J work is required to stretch a spring through 0.1 m. Find the force constant of the spring. If the spring is further stretched through 0.1 m, calculate work done.