Mechanics Revision Exercise

Mechanics Revision Exercise
Q1. Which of the following is/are the direct implication(s) of Newton's first law?
(1) A boy standing on a bus is 'pulled' backwards when the bus starts moving.
(2) On a smooth surface, when you push another person in front of you, you will move backwards.
(3) The balls of different masses reach the ground at the same time in Galileo's experiment (carried out on the tower of Pisa). A (1) only B (2) only C (3) only D (1) and (2) only

Q2. Two objects, connected by a inextensible string, are pulled along a smooth surface.

The pulling force is withdrawn when the string becomes tight. Which of the following statements is correct?
A The string becomes slack as the smaller object travels faster.
B The string remains straight as both objects move with the same velocity due to their inertia.
C The smaller object keeps moving because there is a force pulling it by the larger object.
D The heavier object slows down as it is pulled backwards by the lighter object.
Q3. Box A is placed on box B and the masses of A and B are 5 kg and 10 kg respectively.

If all surfaces are smooth, what are the accelerations of A and B when 15 N applies on B horizontally?

Acceleration of A
Acceleration of B
A
1 m s2
1 m s2
B
0
1.5 m s2
C
1.5 m s2
1.5 m s2
D
0
1 m s2

Q4. A 3-kg box is pushed by a horizontal force of 21 N. The box moves horizontally with an acceleration of 4 m s–2.

What is the frictional force acting on the box? A 6 N B 8 N C 9 N D 12 N

Q5. In the figure below, a 3-kg box is pushed by a horizontal force of 5 N.

If the box does not move, what is the frictional force acting on the box? A 5 N B 9 N C 12 N D less than 5 N

Q6. Two objects A and B are connected by a non-extendable string over a smooth pulley. Object A is pulled along the smooth bench with a force of 23 N.

What is the acceleration of object B? A 1 m s–2 B 7.67 m s–2 C 12.5 m s–2 D 23 m s–2

Q7. Tom gives a sudden push to his toy car of mass 50 g. The car runs on the rough floor at an initial velocity of 2 m s–1 and stops after travelling for a distance of 4 m. Find the average frictional force acting on the car. A 0.01 N B 0.025 N C 0.05 N D 0.1 N

Q8. Which of the following graphs show(s) that a constant resultant force is acting on the object?

(1)

(2)

(3)

A (1) and (2) only B (1) and (3) only C (2) and (3) only D (1), (2) and (3)

Q9. A force Fa applies on a box, which is placed on the floor.

The variation of Fa with time t is shown in the figure below.

If the box does not move, which of the following figures best shows the variation of the magnitude of the friction f with time t?

A

B

C

D

Q10. If a force F applies on an object of mass m1 on a smooth surface, the acceleration of the mass would be 4 m s–2. If another object of mass m2 has acceleration of 7 m s2 when 0.5F applies on it, what is the ratio of m1 to m2? A 1 : 3 B 4 : 7 C 7 : 4 D 7 : 2

Q11. Two objects are connected by a spring balance and then hung to the ceiling as shown below. The string is then cut at the point that the arrow indicates.

Which of the following combinations describing the change of the balance's reading is correct? Before After A 10 N 10 N B 10 N 0 N C 30 N 10 N D 30 N 0 N

Q12. In the figure below, a cannon-ball has been fired from a cannon.

Which of the following figures best shows the direction of the resultant force acting on the cannon-ball at different time?
A

B

C

D

Q13. If the weight of a boy is 750 N on the Earth, what is his weight on Jupiter? (Given: g on Jupiter = 26 m s2) A 750 N B 1950 N C 2880 N D 7500 N

Q14. If forces of 20 N and 30 N act at the same point, what are the greatest and the least resultant force that they can produce?

Greatest
Least
A
36 N
20 N
B
50 N
30 N
C
50 N
10 N
D
70 N
5 N

Q15. An object of mass 0.5 kg is pressed against a smooth wall with a 15-N force. The force is inclined at 30. Find the magnitude of the acceleration of the object.

A 5.0 m s–2 B 7.3 m s–2 C 15.0 m s–2 D 30.0 m s–2

Q16. A ball is put on a smooth table and it is pulled by two forces, one towards north and the other towards east. The plane of the forces and the table surface are horizontal.

In order to keep the ball moving towards east at a constant velocity, an additional force is required. Find the magnitude of the additional force. A 5 N B 13 N C 17 N D 60 N

Q17. In the figure below, a ball of mass m is suspended by two strings. The tension of the strings are T1 and T2. Which of the following statements is/are correct?

(1) T1 cos 60 = T2 cos 30 (2) T1 sin 60 + T2 sin 30 = mg (3) The resultant force of T1 and T2 = mg A (1) and (2) only B (1) and (3) only C (2) and (3) only D (1), (2) and (3)

Q18. In the figure below, a block of mass x kg is suspended by a string and a horizontal force.

If the tension in the string is T, which of the following statements is INCORRECT? A T sin  = F B In order to keep the block stationary, when  increases, F should increase. C T cos  = x D F = 10x  tan 
Q19. In the figure below, a block of mass m1 and a weight of mass m2 are connected by a inextensible string.

If both of them are at rest, which of the following statements is/are correct?
(1) m1 sin  = m2g
(2) If  decreases, the block will move up with uniform acceleration.
(3) If  increases, the normal reaction force that the plane acts on the block will decrease. A (1) and (2) only B (1) and (3) only C (2) and (3) only D (1), (2) and (3)

Q20. A toy car of weigh W is placed on a weighing scale that is fixed in a box. The box is pulled up by a rope at a constant speed from time t1 to t2, and at t2 the rope breaks suddenly.

Which of the following is correct?
A Reading = W before t2, and then drops to zero gradually.
B Reading > W before t2, and then drops to zero gradually.
C Reading = W before t2, and then drops to zero immediately.
D Reading > W before t2, and then drops to zero immediately.

Q21. Jeanie steps onto a weighing scale in a lift and the reading of the scale is 550 N.

If her mass is 45 kg, which of the following statements about the lift is correct? A The lift is moving up with acceleration 2.22 m s2. B The lift is moving down with acceleration 1.8 m s2. C The lift is moving down with deceleration 2.22 m s2. D The lift is moving up with deceleration 1.8 m s2.

Q22. Mary of weight W stands inside a lift. The life is moving upwards at a constant acceleration. Let the normal force exerted on Mary by the floor be R, which of the following statements is/are correct?
(1) R is greater than W in magnitude.
(2) R and W are in opposite directions.
(3) R and W form an action-and-reaction pair according to Newton's third law. A (1) only B (2) only C (1) and (2) only D (2) and (3) only

Q23. A pair of forces FA and FB is indicated in each of the following cases. Which of them is/are the example(s) of action-and-reaction pairs according to Newton's third law?
(1)

 FA = normal reaction acting on the ball by the player
 FB = weight of the ball

(2)

 FA = tension that holds the object
 FB = weight of the object

(3)

 FA = force exerted on the plane by the ejected gas
 FB = force exerted on the ejected gas by the plane

A (2) only B (3) only C (1) and (2) only D (2) and (3) only

Q24. A car moves at 90 km h1 and its mass is 500 kg. If it changes its velocity to in 7 s and the friction acting on it is 700 N, what is its average braking force? A 240 N B 490 N C 1166 N D 1890 N

Q25. In the following figure, two trolleys of mass 2 kg and 3 kg are tied together on a smooth plane and a horizontal force F pulls them.

If the trolleys have an acceleration of 2 m s–2, what are the values of tension T and horizontal force F?

T
F
A
2 N
6 N
B
4 N
6 N
C
6 N
10 N
D
4 N
10 N

Q26. In the following figure, the y-kg block accelerates the x-kg trolley with an acceleration a.

Which of the following expressions is the friction acting on the trolley? A 10y  (x + y)  a B 10y  (y  x)  a C D 10  (x + y)  ya

Q27. A block is rest on an inclined rough surface. If the block remains at rest when two forces of magnitudes 5 N and 2 N acts on it, what is the resultant force acted on the block?

A zero
B 2 N
C 3 N
D 7 N

Q28. Which of the following pairs of forces is NOT an action and reaction pair according to Newton's third law of motion?
A
The weight of a woman siting on a chair and the force supporting on the woman by the chair
B
The gravitational force acting on the Earth by the moon and the gravitational force acting on the moon by the Earth
C
The force exerted by a swimmer on the water to push the water backwards and the force exerted by the water to push the swimmer forwards
D
The friction that slows down a sliding block and the force that drags the ground by the block.

Q29. Three forces F1 , F2 and F3 act on a particle P as shown below. If a fourth force F4 acts on P to keep it in equilibrium, find the magnitude of F4.

Scale: 1cm represents 1 N
A 4.0 N
B 4.2 N
C 4.5 N
D 5.8 N

Q30. Which of the following phenomena can be explained by Newton's first law of motion?
A A passenger in a MTR train tends to move backwards when the train speeds up.
B A coin and a piece of paper fall with the same acceleration in a vacuum.
C A tank recoils when it fires.
D A man weighs less on the Moon than on the Earth.

Q31. A light rope is fixed at points A and B at the same level. A weight is hung at the midpoint C of the rope. The rope depresses such the ACB = 150.

If the mass of the weight is of 200 g, what is the tension in the rope?
A 0.9 N
B 1.9 N
C 3.9 N
D 7.7 N

Q32. In the following figure, ball A of mass 2m and ball B of mass 3m fall from the height of h and 3h respectively.

What is the ratio of the maximum velocity of A to that of B?
A 1 : 3
B 2 : 3
C
D

Q33. In the following figure, a 0.01-kg bullet travelling at a speed of 600 m s-1 penetrates a 10-cm wooden block.

If the bullet emerges from the block at 450 m s-1, what is the average resistance of the wooden block? Assume the air resistance is negligible.
A 6542 N
B 7875 N
C 8735 N
D 9560 N

Q34. A car of mass 1500 kg travels with constant velocity 40 km h-1. If the friction and air resistance are negligible, what is the work done required to accelerate to 60 km h-1?
A 95 kJ
B 103 kJ
C 108 kJ
D 116 kJ

Q35. The above figure shows a section of a roller-coaster. When a 1500-kg cart passes A, its speed is 0.5 m s1. If the distance along the rail between A and B is 200 m and the average frictional force acting on the cart is 400 N, what is the speed of the cart at B?

A 5.6 m s1 B 9.67 m s1 C 12.3 m s1 D 14.4 m s1

Q36. A ball of mass m kg rebounds from the ground several times after it falls vertically from a height of h m. If it loses 10% of total energy after each bounce, what is the maximum speed of the ball just after the fourth bounce? A m s1 B m s1 C m s1 D m s1
Q37. The following figure shows a simple pendulum. The pendulum bob has a mass of m kg and it is pulled to one side. When the bob is released, it swings to and fro.

Which of the following statements is/are correct? (1) The potential energy of the bob at A is larger than that at B by mgh. (2) The speed of the bob at B is the highest in the whole cycle. (3) The pendulum string does work on the bob. A (1) only. B (2) only. C (1) and (2) only. D (1), (2) and (3).

Q38. A bullet of mass 40 g travels horizontally. It hits a wooden block at 330 m s1 and comes out of the block at 208 m s1. If it takes the bullet 0.1 s to penetrate the block, what is the energy loss of the bullet? A 865 J B 1310 J C 2178 J D 13 100 J

Q39. Which of the following expressions is NOT equal to power? A B Force  velocity C Weight  displacement D

Q40. In a marathon, the winner and the runner-up have the same mass. Compared with the runner-up, the winner has more A kinetic energy. B potential energy. C force. D power.

1. A
2. B
3. B
4. C
5. A
6. A
7. B
8. C
9. C
10. D
11. B
12. A
13. B
14. C
15. A
16. B
17. D
18. C
19. D
20. C
21. A
22. C
23. B
24. B
25. D
26. A
27. A
28. A
29. C
30. A
31. C
32. C
33. B
34. D
35. B
36. B
37. C
38. B
39. C
40. D