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Class 9

Explore popular questions from Force and Law of Motion for Class 9. This collection covers Force and Law of Motion previous year Class 9 questions hand picked by experienced teachers.

Force and Law of Motion

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Q 1. A shell of mass 0.020 kg is fired by a gun of mass 100 kg If the muzzle speed of the shell is 80 m/s, the recoil speed of the gun -

A

14 m/s

B

0.012 m/s

0.016 m/s

D

100 m/s

Explanation

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Q 2. Two billiard balls each of mass 0.05 kg moving in opposite directions with speed 6 m/s collide and rebound with the same speed The magnitude of impulse imparted to each ball due to the other -

0.6 kg m/s

B

zero

C

6 kg m/s

D

none of these

Explanation

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Q 3. Assertion: Large force is required to move a body uniformly along a straight path
Reason: A body moving with uniform acceleration has a constant force acting on it

A

Both Assertion and Reason are true and Reason is the correct explanation of 'Assertion'

Both Assertion and Reason are true and Reason is not the correct explanation of 'Assertion'

C

Assertion is true but Reason is false

D

Assertion is false but Reason is true

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Q 4. Which of the following statements is/are not correct ?

A force is needed to keep a particle moving along a straight line with uniform velocity

B

The same force for the same time causes the same change in momentum for different bodies

C

Frictional force opposes both motion as well as relative motion

D

It is not motion, but relative motion that the frictional force opposes

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Q 5. A force of 50 dynes is acted on a body of mass 5g which is at rest for an interval of 3sec. The impulse is

A

{tex}{0.15}\times{10^{-3 }}{/tex}Ns

B

{tex}{0.98}\times{10^{-3 }}{/tex}Ns

{tex}{1.5}\times{10^{-3 }}{/tex}Ns

D

{tex}{2.5}\times{10^{-3 }}{/tex}

Explanation

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Q 6. A force of 100 N acts on 50 kg for 2 seconds The same force acts on 25 kgs for 2 seconds The ratio of the momenta produced and the accelerations caused in two bodies respectively are -

A

1 : 1, 2 : 1

1 : 1, 1 : 2

C

1 : 2, 1 : 1

D

none of these

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Q 7. The driver of a three-wheeler moving with a speed of 36 km/h sees a child standing in the middle of the road and brings his vehicle to rest in 4.0 s just in time to save the child The average retarding force on the vehicle? The mass of the three-wheeler is 335 kg and mass of the driver is 65 kg

A

1025 N

B

10 N

1000 N

D

none of these

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Q 8. A horizontal force of 600 N pulls two masses 10 kg and 20 kg (lying on a frictionless table) connected by a light string The tension in the string , if the 20 kg mass is pulled

200 N

B

400 N

C

100 N

D

50 N

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Q 9. Two masses 8 kg and 12 kg are connected at the two ends of a light inextensible string that goes over a frictionless pulley The acceleration of the masses, when the masses are released is (g = 10 m/s2)

A

{tex}6 m/s^2{/tex}

B

{tex}4 m/s^2{/tex}

C

{tex}10 m/s^2{/tex}

{tex}2 m/s^2{/tex}

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Q 10. Assertion: A player lowers his hands while catching a ball Reason: Impulse is the time rate of change of momentum

A

Both Assertion and Reason are true and Reason is the correct explanation of 'Assertion'

B

Both Assertion and Reason are true and Reason is not the correct explanation of 'Assertion'

Assertion is true but Reason is false

D

Assertion is false but Reason is true

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Q 11.

Column IColumn II
(A) Measure of inertia(P) Force × time
(B) Impulse(Q) Mass × velocity
(C) Momentum(R) Mass × acceleration
(D) Newton's second law of motion(S) Mass

A

(A)-(S), (B)-(P), (C)-(Q), (D)-(R)

B

(A)-(R), (B)-(Q), (C)-(P), (D)-(S)

C

(A)-(R), (B)-(P), (C)-(Q), (D)-(S)

(A)-(S), (B)-(Q), (C)-(P), (D)-(R)

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Q 12. If a body is in equilibrium under a set of non-collinear forces, the minimum number of forces has to be:

A

Four

Three

C

Two

D

Five

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Q 13. Bullets of 0.03 kg mass each hit a plate at the rate of 200 bullets per second, with a velocity of 50 m/sec reflect back with a velocity of 30 m/sec The average force acting on the plate, in newtons is:

A

120

B

180

C

300

480

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Q 14. A force of 5 N making an angle {tex}\theta{/tex} with the horizontal acting on an object displaces it by 0.4 m along the horizontal directionIf the object gains kinetic energy of 1 J, the horizontal component of the force is:

A

1.5 N

2.5 N

C

3.5 N

D

4.5 N

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Q 15. A force of 50 dynes is acted on a body of mass 5g which is at rest for an interval of 3sec The impluse is

A

{tex}0.15 \times 10^{-3} \, Ns {/tex}

B

{tex}0.98 \times 10^{-3} Ns{/tex}

{tex}1.5 \times 10^{-3} Ns{/tex}

D

{tex}2.5 \times 10^{-3}Ns{/tex}

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Q 16. Swimming is possible by the:

A

first law of motion

B

second law of motion

third law of motion

D

Newtons law of gravition

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Q 17. A cricket player catches a ball of mass 0.1 kg, moving with a speed 10 m/s in 0.1 second Froce exerted by him is (N)

A

4

B

2

C

1

10

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Q 18. Newton's first law of motion defines

Force

B

Angular Velocity

C

Momentum

D

Acceleration

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Q 19. Which of the following statements is/are correct ?

Momentum has both direction and magnitude

B

Momentum is a vector quantity

C

The SI unit of acceleration is metre per second squared

D

The rate of change of momentum of an object is not in the direction of force

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Q 20. Action-Reaction forces act

A

on the same body

on the different bodies

C

along different lines

D

in the same direction

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Q 21. A constant force acts on an object of mass 4 kg for a duration of 1 second It increases the object velocity from {tex}4 \, ms^{-1}{/tex} to {tex}6 \, ms^{-1}{tex}. Select the correct options

Magnitude of the applied force is 8 N

B

Final velocity of the object if the force applied for 5 sec is 24 m/s

C

Change in momentum in 1 sec is 10 kg m/s

D

Change in momentum of object during 5 sec is 56 kg m/sec

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Q 22. A girl of mass 30 kg jumps with a horizontal velocity of 4 m/s onto a stationary cart with frictionless wheels The mass of cart is 2 kg Select the correct options (Assuming that there is no external unbalanced force working in the horizontal direction)

The total momentum of the girl and the cart before the interaction is 120 kg m/s

B

The total momentum of the girl and the cart after the interaction is 140 kg m/s

C

The girl on cart will move with a velocity 15 m/s in the direction in which the girl jumped

D

The girl on cart will move with a velocity 15/4 m/s in the opposite direction in which the girl jumped

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Q 23.

Column IColumn II
(A) A rocket works on the principle of(P) First law of motion
(B) Recoiling of gun can be explained by(Q) Second law of motion
(C) The law which defines the force is(R) Third law of motion
(D) The law which gives the quantitative(S) Conservation of momentum measurement of force is

A

(A)- (R), (B)-(S), (C)-(P), (D)-(Q)

B

(A)- (P,R), (B)-(R), (C)-(Q), (D)-(D)

(A)- (R,S), (B)-(R,S), (C)-(P), (D)-(Q)

D

(A)- (Q), (B)-(R), (C)-(P), (D)-(S)

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Q 24. A force of 100 N acts on 50 kg for 2 seconds. The same force acts on 25 kgs for 2 seconds. The ratio of the momenta produced and the accelerations caused in two bodies respectively are -

A

1 : 1, 2 : 1

1 : 1, 1 : 2

C

1 : 2, 1 : 1

D

None of these

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Q 25. The driver of a three-wheeler moving with a speed of 36 km/h sees a child standing in the middle of the road and brings his vehicle to rest in 4.0 s just in time to save the child. The average retarding force on the vehicle? The mass of the three-wheeler is 335 kg and mass of the driver is 65 kg.

A

1025 N

B

10 N

1000 N

D

None of these