Force and laws of motion Class 9 Science Multiple Choice Questions & Answers

Question-1. A carpenter exerts a force of magnitude 1.5 N at right angles to the surface of a nail of mass 3 gram to drive it into the wood. If wood offers a resistive force of 0.6 N and the time of interaction of hammer and the nail 0.01 s, the depth through which the nail penetrates is

1. 1.5 mm
2. 15m
3. 1.5 cm
4. 15 cm

Question-2. A gas behaves like an ideal gas under conditions of

1. Low pressure and low temperature
2. High pressure and low temperature
3. High temperature and high pressure
4. Low pressure and high temperature

Question-3. A gas deviates from ideal behaviour at a high pressure because its molecules

1. Are bound by covalent bonds
2. Show the Tyndall effect
3. Have kinetic energy
4. Attract one another

Question-4. A gun of mass 5kg fires 50gm bullet with a velocity of 200m/s. Find the recoils velocity of the gun.

1. 0.2m/s
2. -2 m/s
3. 20 m/s
4. Zero

Question-5. A man wearing a bullet-proof vest stands on roller skates. The total mass is 80 kg. A bullet of mass 20 g is fired at 400 m/s. It is stopped by the vest and falls to the ground. What is then the velocity of the man?

1. 0 m/s
2. 1 m/s
3. 0.1 m/s
4. 0.01 m/s

Question-6. A passenger in a moving train tosses a coin which falls

1. Will not move
2. Behind him
3. In front of him
4. Falls outside the train

Question-7. A plate, a ball and a child all have the same mass. The one having more inertia is the

1. All have equal inertia
2. plate
3. ball
4. child

Question-8. A real gas at a very high pressure occupies

1. Cannot be predicted
2. Less volume then that of an ideal gas under identical condition
3. More volume than that of an ideal gas under identical conditions
4. Same volume than that of an ideal gas under identical conditions

Question-9. Acceleration acts always in the direction

1. of the final velocity
2. of the displacement
3. of the initial velocity
4. of the net force

Question-10. According to the kinetic energy of gases, in an ideal gas, between two successive collisions a gas molecules travels

1. with an accelerated velocity
2. in a circular path
3. in a wavy path
4. in a straight line path

Question-11. An ideal gas expands according to PV = constant. On expansion,the temperature of gas

1. cannot be determined because the external pressure is not known
2. will rise
3. will drop
4. will remain constant

Question-12. An object of mass 20 kg is moving with a velocity of 10 m/s. Its momentum will be

1. 200 kg.m/s
2. 2000 kg.m/s
3. 20 kg.m/s
4. 2 kg.m/s

Question-13. An object of mass 6 kg is sliding on horizontal surface, with a uniform velocity of 8 m/ s . Assuming force of friction offered by the surface to be zero, The force required to maintain the motion of object with the same uniform velocity is

1. 32 Newtons
2. 0 Newton
3. 2 Newtons
4. 8 Newtons

Question-14. An object will continue to accelerate until

1. The resultant force on it is increased continuously.
2. The resultant force begins to decrease.
3. The resultant force on it is zero.
4. The velocity changes direction.

Question-15. Change in momentum when a car weighing 700kg changes its speed from 100m/s to 200 m/s is

1. 70000 kg.m/s
2. 14000 kg.m/s
3. 10500000 kg.m/s
4. 21000000 kg.m/s

Question-16. Essential characteristic of equilibrium is

1. none of the above
2. K. E equals zero
3. acceleration equals zero
4. momentum equals zero

Question-17. Force required in accelerating a 2 kg mass at 5 m/s2 and a 4 kg mass at 2 m/s2

1. Zero in both the cases
2. 2kg mass at 5m/s2 is less than 4 kg mass at 2 m/s2
3. Same in both the cases
4. 2kg mass at 5m/s2 is greater than 4 kg mass at 2 m/s2

Question-18. Formula to find the Force is

1. a=Fm
2. F= ma
3. F= m/a
4. F= a/m

Question-19. Friction is

1. none of them.
2. useful to us
3. harmful to us
4. both useful as well as harmful to us

Question-20. Frictional force

1. always in the direction of motion
2. always in the opposite director of motion
3. always opposes motion of a body
4. always opposes relative motion between the surfaces of contact

Question-21. If a bus starts suddenly, the passengers in the bus will tend to fall

1. None of the above.
2. In the direction opposite to the direction of motion of bus.
3. In the same direction as the direction of motion of bus.
4. Sideways.

Question-22. If an object moves with a uniform velocity we can conclude that

1. it has uniform acceleration
2. there is no force acting on the body
3. no unbalanced force acts on it
4. an unbalanced force acts on the body

Question-23. If the four tubes of a car are filled to the same pressure with N2, O2, H2 and Ne separately, then which one will be filled first ?

1. N2
2. O2
3. H2
4. Ne

Question-24. Inertia is a measure of

1. acceleration
2. Mass
3. velocity
4. Force

Question-25. Inertia is a property of a body by virtue of which the body is

1. Unable to change by itself the state of rest or uniform motion in a straight line.
2. Unable to change by itself the state of rest.
3. Unable to change by itself the state of uniform motion in a straight line.
4. Unable to change by itself the direction of motion.

Question-26. It is easter to liquefy oxygen than hydrogen because

1. Oxygen has a lower critical temperature and higher inversion temperature than hydrogen
2. Oxygen has a higher critical temperature and a higher inversion temperature than hydrogen
3. The critical temperature and inversion temperature of oxygen is very low
4. Oxygen has a higher critical temperature and lower inversion temperature than hydrogen

Question-27. Qualitative definition of Force is given by

1. Newtons law of gravitation
2. Newtons first law of motion
3. Newtons Second law of motion
4. Newtons third law of motion

Question-28. Rocket works on the principle of conservation of

1. velocity
2. Energy
3. Mass
4. momentum

Question-29. Some assumptions from the kinetic molecular theory are listed below. Which one is most frequently cited to explain Charle's law ?

1. The average kinetic energy of gas articles is proportional to the Kelvin temperature
2. Collisions of gas particle are elastic and total kinetic energy of the gas is constant
3. A gas consists of tiny particles moving in random straight line motion
4. The volume of the particle is negligible compared to the volume of the gas

Question-30. Temperature according to kinetic theory, is a measure of

1. Volume f gas
2. Average translational kinetic energy of gas molecules
3. Intermolecular attraction
4. Intermolecular distances

Question-31. The acceleration of an object is

1. all of the above
2. inversely proportional to its mass
3. directly proportional to the applied force
4. resisted by inertia

Question-32. The action and reaction forces referred to in the third law

1. Need not be equal in magnitude but act in the same direction
2. Must act on different objects
3. Must act on the same objec
4. May act on different objects

Question-33. The relation between acceleration, mass and force is given by

1. a = F/m
2. a x F = m
3. F = m/a
4. F x m = a

Question-34. The S.I. unit of force is

1. Newton per square metre
2. Newton-metre
3. Newton
4. Newton per second

Question-35. The seat belts are provided in the cars so that if the car stops suddenly due to an emergency braking, the persons sitting on the front seats are not thrown forward violently and saved from getting injured. Can you guess the law due to which a person falls in forward direction on the sudden stopping of the car?

1. Newton?s law of gravitation
2. Newtons first law of motion
3. Newton?s second law of motion
4. Newton?s third law of motion

Question-36. The temperature at which real gases obey the ideal gas laws over a wide range of pressure is called

1. Reduced temperature
2. Critical temperature
3. Boyle temperature
4. Inversion temperature

Question-37. The term that accounts for intermolecular force in van der Waal's equation for non ideal gas is

1. (RT)?1
2. RT
3. V ? b
4. (P +a/V2)

Question-38. There will be a change in the speed or in the direction of motion of a body when it is acted upon by

1. Zero Force
2. An Unbalanced force
3. Balanced Force
4. Uniform force

Question-39. Two equal masses m each moving in the opposite direction with the same speed v collide and stick to each other. The velocity of the combined mass is

1. zero
2. v
3. 2v
4. v/2

Question-40. Type of inertia that tends to resist the change in case of an -Athlete often jumps before taking a long jump

1. Uniformly accelerated motion
2. Inertia of motion
3. Inertia of rest
4. Inertia of direction

Question-41. Under which of the following conditions, Van der Waal's gas approaches ideal behaviour ?

1. Low temperature
2. Extremely low pressure
3. High pressure
4. Low product of PV

Question-42. Universal gas constant (R) is divided by Avogadro's number (N0) then the value is equivalent to

1. Boltzmann's constant
2. van der Waal's constant
3. Rydberg's constant
4. Planck's constant

Question-43. What is the momentum of a body of mass 2m and velocity v/2?

1. mv/2
2. mv/4
3. mv
4. 2mv

Question-44. When a 12 N force acts on 3 kg mass for a second, the change in velocity is (in m/s)

1. 18
2. 36
3. 4
4. 2

Question-45. When a bus starts suddenly from rest, the passengers sitting inside the bus move backwards. This illustrates an example of

1. None of these
2. Newton First Law of Motion
3. Newton Second Law of Motion
4. Newtons Third Law of Motion

Question-46. When a force is exerted on an object, it can change its

1. All the above
2. State
3. Position
4. Shape

Question-47. When no external force acts on an object, the physical quantity that remains conserved is

1. force
2. velocity
3. momentum
4. acceleration

Question-48. When the temperature is raised, the viscosity of the liquid decreases.This is because

1. Increase in temperature increases the average kinetic energy of the molecules which over-comesthe attractive force between them
2. Attraction between the molecules increases
3. Covalent and hydrogen bond forces decrease
4. Volume of the solution decreases

Question-49. When unbalanced forces act on a body, the body

1. Must move in a curved path
2. Must move with uniform velocity
3. Must remain at rest
4. Must experience acceleration

Question-50. Which of the following gases has the lowest average speed at 25°C ?

1. H2S
2. NH3
3. O2
4. CH4

Question-51. Which of the following has the largest momentum?

1. A car parked in a parking lot.
2. A cat running down the street
3. A pickup truck travelling down the highway.
4. A large truck parked in a parking lot.

Question-52. Which of the following is the unit of linear momentum?

1. kg
2. kg m/s
3. kg ms
4. kgms-2

Question-53. Which of the following situations involves the Newton?s second law of motion?

1. A force exerted by the escaping air from a balloon in the downward direction makes the balloon to go upwards
2. A force can stop a lighter vehicle as well as a heavier vehicle which are moving
3. A force exerted by a lighter vehicle on collision with a heavier vehicle results in both the (vehicles coming to a standstill
4. A force can accelerate a lighter vehicle more easily than a heavier vehicle which are moving

Question-54. . Rate of change of momentum is equal to

1. Impulse
2. Acceleration
3. Work done
4. Force

Question-55. A ball is thrown vertically upward in a train moving with uniform velocity. The ball will

1. fall on the left of the thrower
2. fall behind the thrower
3. fall ahead of the thrower
4. return back to the thrower

Question-56. A goalkeeper in a game of football pulls his hands backwards after holding the ball shot at the goal. This enables the goalkeeper to

1. decrease the rate of change of momentum
2. exert larger force on the ball
3. reduce the force exerted by the balls on the hands
4. increase the rate of change of momentum

Question-57. A man is standing on a boat in still water. If he walks towards the shore, then the boat will

1. none of these
2. move away from the shore
3. move towards the shore
4. remain stationary

Question-58. A passenger in a moving train tosses a coin which falls behind him. It means that motion of the train is

1. along circular tracks
2. accelerated
3. uniform
4. retarded

Question-59. A water tanker filled up to (frac{2}{3}) of its height is moving with a uniform speed. On a sudden application of brakes, the water in the tank would

1. rise upwards
2. move backward
3. move forward
4. be unaffected

Question-60. According to the third law of motion, action and reaction

1. act on either body at normal to each other
2. always act on the same body
3. always act on different bodies in opposite directions
4. have same magnitude and directions

Question-61. An object of mass 2 kg is sliding with a constant velocity of 4 ms-1 on a frictionless horizontal table. The force required to keep the object moving with the same velocity is

1. 8 N
2. 32 N
3. 0 N
4. 2 N

Question-62. If the mass of a body is doubled and its velocity becomes half, then the linear momentum of the body will

1. become four times.
2. remain same
3. become double
4. become half

Question-63. Inertia is the property of a body by virtue of which, it cannot change by itself

1. all of these.
2. its state of rest
3. its steady state of uniform motion
4. its direction of motion

Question-64. Rocket works on the principle of conservation of

1. velocity
2. mass
3. energy
4. momentum

Question-65. The inertia of an object tends to cause the object

1. to decelerate due to friction
2. to increase its speed
3. to decrease its speed
4. to resist any change in its state of motion

Question-66. What is a force, which always opposes the motion of one body over the other body in contact with it

1. Frictional force
2. Gravitational force
3. Reaction force
4. Normal force

Question-67. When a number of forces acting simultaneously on a body bring about a change in its state of rest or of uniform motion in a straight line, then these forces acting on the body are said to be

1. opposite forces
2. balanced forces
3. equal forces
4. unbalanced forces

Question-68. When we stop pedalling, the bicycle begins to slow down. This is because of the

1. Nature of the bicycle to stop after some time
2. Frictional force acting along the direction of motion of bicycle
3. Air resistance which is in the direction of motion
4. Frictional force acting opposite to the direction of motion of bicycle by the road

Question-69. Which of the following is an incorrect statement?

1. Newton?s third law talks about the direction of the force.
2. Mass is measure of inertia of a body.
3. Newton?s first law of motion is the law of inertia.
4. Unbalanced force produces constant velocity.

Question-70. Which of the following is not an application of conservation of linear momentum?

1. A body suspended from the hook of a spring balanced in a lift which is accelerated downward
2. While firing a bullet, the gun must be held tight to the shoulder
3. When a man jumps from a boat to the shore
4. A rocket explodes on midway from the ground

Question-71. Which of the following statements is not correct for an object moving along a straight path in an accelerated motion?

1. A force is always acting on it
2. Its speed keeps changing
3. Its velocity always changes
4. It always goes away from the Earth

Question-72. A bullet of mass 20gm is fired from a gun of mass 8kg with a velocity of 400 m/s, calculate the recoil velocity of gun

1. -1m/s
2. -2m/s
3. 1m/s
4. 2m/s