# Force & laws of Motion Conceptual Questions and MCQ

Given below are the force and laws of motion class 9 conceptual questions and MCQ
(a) Objective Type Questions
(b) True and false
(c) Short questions
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## Multiple choice questions

Question 1
Why a goalkeeper in a game of football pulls his hands backwards after holding the ball shot at the goal?
a.Keep the ball in hands firmly
b.Reduce the force exerted by the ball
c.To exert larger force on the ball
d. None of these

Question 2
A IITJEE text book of mass M rests flat on a horizontal table of mass m placed on the ground. Let Rx->y be the constant force exerted by the body x on body Y. According to Newton third law, which of the following is an action-reaction pair of forces?
a. (M+m)g and Rtable->book
b. Rground->table and mg+Rbook->table
c. Rground->table and Rtable->ground
d.   Mg and Rtable->book

Question 3
what options are true about momentum
a. Momentum is a vector quantity
b. The Unit of Momentum is kgm/s
c. Momentum is a scalar quantity
d. When two bodies acts on each other and no external force is acting on the system, then the momentum remains constant

Question 4
What is not true of unbalanced forces?
a. It can change the velocity of the object
b. It can change the direction
c. Change the momentum
d. Change the shape of the body

Question 5
An object of mass 100kg is accelerated uniformly from a velocity of 4 m/s to 8 m/s in 2 seconds. Calculate the initial and final momentum of the object
a. 400 kgm/s,800 kgm./s
b. 100 kgm/s,400 kgm./s
c. 200 kgm/s,400 kgm./s
d. 400 kgm/s,400 kgm./s

Question 6
Find the magnitude of the force exerted on the object in the above question?
a. 250N
b. 50N
c.100N
d. 200 N

Question 7
Which are laws of Newton’s ?
a. Law stating action and reaction are equal and opposite
b. Product of mass and acceleration.
c. Tendency of a body to oppose any change in its state of rest or uniform motion
d. All the above

Question 8
Which of the followings works on the principle of momentum?
a. A gun recoils after firing
b. Rocket
c. The case of hose pipe
d. All the above

Question 9
A boy of mass 50 Kg running at 5 m/s jumps on to a 20Kg trolley travelling in the same direction at 1.5 m/s. What is the common velocity?
a. 4m/s
b. 3 m/s
c. 3.5 m/s
d. None of the above

Question 10
which of these are vector quantities?
a. momentum
b. Force
c. Impulse
d. Inertia

1. b
2. c
3. a,b,d
4. d
5. a
Initial momentum =$mv_i =100 \times 4=400$ kgm/s
Final Momentum = $m_f=100 \times 8=800$ kg/s
6. d
$a = \frac {\Delta v}{t}=\frac {8-4}{2}=2$ m/s2
$Force=mass \times acceleration=100 \times 2=200$ N

7. d
8. d
9. d
Since no external force, law of conservation of momentum can be applied
Initial Momentum
$p_i =50 \times 5+ 20 \times 1.5=280$ kgm/s
Final momentum $p_f= 70 \times v=70v$ where v is the common velocity
Now we know that
Initial momentum=Final momentum
$280=70v$
V=4m/s

10. (a),(b) and (c)

## True and False

Question 11
True and False Statements
A. Momentum is a vector quantity
B. Rate of change of momentum is called Force
C. Inertia is that property of a body due to which it resists a change in its state of rest or of uniform motion
D. when a bullet is fired from the Gun and gun recoil. This is based on law of inertia
E. The unit of momentum is Kg-m
F. Force is a scalar quantity
G. Action -Reaction pair of force act on different body
I. A object can still run with non-zero velocity event the net force acting on the body is zero

A. True
B. True
C. True
D. False
E. False
F. False
G. True
I. True

Question 12
What is impulse? Prove that Impulse is equal to change in momentum?

Question 13
State all the law Newton's law of Motion? And Give example for each law

Question 14
What is the law of conservation of Momentum? A car of mass 200 kg moving with 3m/s collides with another car of mass 300 Kg moving in the same direction at 2 m/s .They collide and move together after that. What is the common velocity?

Question 15
According to the third law of motion when we push on an object, the object pushes back on us with an equal and opposite force. If the object is a massive truck parked along the roadside, it will probably not move. A student justifies this by answering that the two opposite and equal forces cancel each other. Comment on this logic and explain why the truck does not move?

The logic is that Action and Reaction always act on different bodies, so they can not cancel each other. When we push a massive truck, the force of friction between its tyres and the road is very large and so the truck does not move

Question 16
Arrange the items in order of increasing inertia?
Bicycle, bus, Train, car, Scooter

Bicycle > Scooter > car> bus> train

Question 17
Explain these statements
a. when an cyclist moving stop pedaling ,Cycle get stops after some time. Which force is responsible for stopping
b. Why people sitting in bus fall backward when bus suddenly starts?
c. A karate player can break a pile of tiles with a single blow of his hand?
d. When a hanging carpet is beaten with stick ,the dust particle start coming out of it?

(a) Force of friction opposes the motion and stops the cycle
(b)This is because of inertia, the people tends to remain in a state of rest even when the bus start moving
(c) This is because the karate player moves his hand very fast ,This way  large momentum of fast moving hand  reduces to zero in very short time and this result in very high force on the slab and they break
(d)This is because force of stick moves the carpet but dust due to inertia remains at rest and start coming out

Question 18
A batsman hits a cricket ball which then rolls on a level ground. After covering a short distance, the ball comes to rest. The ball slows to a stop because
(a) the batsman did not hit the ball hard enough.
(b) velocity is proportional to the force exerted on the ball.
(c) there is a force on the ball opposing the motion.
(d) there is no unbalanced force on the ball, so the ball would want to come to rest.

Ball comes to rest because of frictional force.Hence (c) is the correct option

Question 19
In the following example, try to identify the number of times the velocity of the ball changes:
"A football player kicks a football to another player of his team who kicks the football towards the goal. The goalkeeper of the opposite team collects the football and kicks it towards a player of his own team".
Also identify the agent supplying the force in each case.

The velocity of the ball changes four times.
a. When a football player kicks the football, its speed changes from zero to a certain value.In this case, force applied by player helps to change the velocity of the ball.This at first changes the velocity of the ball.
b. Another player kicks the ball towards the goal post. This changes the direction of the ball. Therefore, its velocity also changes. In this case, the player applied a force to change the velocity of the ball. The velocity of the ball has changed 2nd time
c. The goalkeeper collects the ball. In other words, the ball comes to rest. Thus, its speed reduces to zero from a certain value. The goalkeeper applied an opposite force to stop/change the velocity of the ball.Hence, its velocity changes third time.
d. The goalkeeper kicks the ball towards his team players. Hence, the speed of the ball increases from zero to a certain value. Hence, its velocity changes once again. In this case, the goalkeeper applied a force to change the velocity of the ball.

## Summary

This MCQ and Conceptual Questions on Force & laws of Motion Class 9 Physics is prepared keeping in mind the latest syllabus of CBSE . This has been designed in a way to improve the academic performance of the students. If you find mistakes , please do provide the feedback on the mail.
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