Class 9-Physics Force and Laws of MotionContact Number: 9667591930 / 8527521718

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A feild gun of mass 1.5 tonne fires a shell of mass 15 kg with a velocity of $150\mathrm{m}{\mathrm{s}}^{-1}$. Calculate the velocity of the recoil of the gun.

1. $1\mathrm{m}{\mathrm{s}}^{-1}$

2. $1.5\mathrm{m}{\mathrm{s}}^{-1}$

3. $3\mathrm{m}{\mathrm{s}}^{-1}$

4. $5\mathrm{m}{\mathrm{s}}^{-1}$

An astronaut with all her equipments has a mass of 95 kilograms. How mush will she weight on the moon, where the acceleration due to gravity is 1.67 meter oer second square?

1. 159 N

2. 169 N

3. 149 N

4. 100 N

A rocket-driven sledge speeds up from 40 meters per second to 55 meters in 5.0 seconds, using an engine that produces 3500 newtons of thrust. How much thrust would be needed to get the same increases in speed in 2.0 seconds

1. 8550

2. 8750

3. 8700

4. 8500

What force must the breaks apply to 2800 kg truck going 30 meters per second to bring it to rest in 8.0 seconds?

1. 12000 N

2. 13000 N

3. 10500 N

4. 12500 N

An unbalanced force acts on body. The body

1. must remain in same state

2. must move with uniform velocity

3. must be accelerated

4. must move along a circle

Choose the wrong statement.

1. Unit of force is newton

2. Force changes shape of body

3. Force is always conserved

4. Force is vector quantity

Balanced forces may ........ a body.

1. move

2. accelerated

3. retard

4. deform

A number of forces acting on a body changes velocity of the body. The forces are

1. parallel

2. unbalanced

3. balanced

4. inclined

External forces are

1. always balanced

2. never balanced

3. may or may not be balanced

4. none of these

Which of the following is the unit of weight?

1. kg

2. quintal

3. newton

4. ton

Choose correct statement.

1. Action and reaction forces act on same object

2. Action and reaction forces act on different object

3. both (1) and (2) are possible

4. Neither (1) nor (2) is correct

A cannon after firing recoils due to

1. Conservation of energy

2. Newton's third law of motion

3. Newton's first law of motion

4. none of these

A man is standing on a boat in still water. If he walks towards the shore the boat will

1. move away from the shore

2. remain stationary

3. move towards the shore

4. sink

A force of $2\times {10}^{5}$N acts on a body of mass $4\times {10}^{4}$kg at rest for 10s. The final velocity of the body is

1. $5m{s}^{-1}$

2. $50m{s}^{-1}$

3. $150m{s}^{-1}$

4. $250m{s}^{-1}$

A bullet is fired horizontally and gets embedded in a block kept on a table. If table is frictionless, then

1. kinetic energy is conserved

2. momentum is conserved

3. Both (1) and (2)

4. None of these

Newton's second law of motion gives us a measure of

1. force

2. inertia

3. mass

4. acceleration

How much force acts on a body whose momentum is constant (i.e. =constant)?

1. zero

2. p/2t

3. 2p/t

4. none

Two forces ${F}_{1}=20$ N and ${F}_{2}=30$ Nare acting on an object as shown in figure.

What is the net force acting on the object?

1. 50 N

2. 10 N

3. 40 N

4. 25 N

How much momentum will a dumb-bell of mass 10 kg transfer to the floor if it falls from a height of 80 cm? Take its downward acceleration to be 10 m ${s}^{-2}$

1. 10 kg m ${s}^{-1}$

2. 20 kg m ${s}^{-1}$

3. 35 kg m ${s}^{-1}$

4. 40 kg m ${s}^{-1}$

A body is accelerated ina straight line. The unbalanced force acts

1. in the direction of motion of the body

2. in a direction opposite to the direction of motion of the body

3. in a direction perpendicular to the direction of motion of the body

4. none of these

The principle of conservation of linear momentum states that the linear momentum of a system

1. cannot be changed

2. cannot remains constant

3. can be changed if only internal forces act

4. can be changed if only external forces act

The mass and speed of four bodies are

Body Mass Speed

A 1 kg 10 m ${s}^{-1}$

B 2 kg 9 m ${s}^{-1}$

C 3 kg 8 m ${s}^{-1}$

D 4 kg 7 m ${s}^{-1}$

The body with the largest magnitude of momentum is

1. A

2. B

3. C

4. D

A person is standing in an elevator. In which situation he finds his weight less than actual, when

1. The elevator moves upward with consultant acceleration

2. The elevator moves downward with constant acceleration

3. The elevator moves upward with uniform velocity

4. The elevator moves downward with uniform velocity

A body whose momentum is constant, must have constant

1. Force

2. Velocity

3. acceleration

4. All of these

A body of mass m kg starts from rest and travels a distance of s m in t seconds. The force acting on it is

1. $\frac{2ms}{{t}^{2}}N$

2. $\frac{ms}{t}N$

3. $\frac{m{s}^{2}}{2t}N$

4. $\frac{m{s}^{2}}{t}N$

A mass of 100 g strikes the wall with speed 5 m ${s}^{-1}$ atr an angle as shown in figure and it rebounds with the same speed. If the contact time is $2\times {10}^{-3}$ sec, what is the force applied by the wall?

1. $250\sqrt{3}N$ to right

2. 250 N to right

3. $250\sqrt{3}$N to left

4. 250 N to left

A rocket of mass 1000 kg exhausts gases at a rate of $4kg{s}^{-1}$ with a velocity 3000 m ${s}^{-1}$. The thurst developed on the rocket is

1. 12000 N

2. 120 N

3. 800 N

4. 200 N

A body at rest explodes into two equal parts. Then

1. they move with different speeds in different directions

2. they move with different speeds in same directions

3. they move with same speed in same direction

4. they move with same speed in different direction

A gun if mass 1 kg fires 4 bullets per sec each of mass 20 g with a velocity 300 m ${s}^{-1}$. The force required to hold the gun is

1. 24 N

2. 28 N

3. 32 N

4. 10 N

Galileo's law of inertia is another name for Newton's .............. law of motion.

1. first

2. third

3. second

4. any one of the above

The 35 kilogram girl is standing on a 20 kilogram wagon a kick that sends it off at 3.8 meters per second. How fast is the girl moving?

1. $1.2m{s}^{-1}$

2. $3m{s}^{-1}$

3. $4m{s}^{-1}$

4. $2.2m{s}^{-1}$

9.8 N is equal to

1. 1 kgf

2. 1 kgwt

3. both (a) and (b)

4. neither (a) nor (b)

A body of mass 5 kg undergoes a change in speed from $20m{s}^{-1}$. The momentum

1. increases by 99 kg m ${\mathrm{s}}^{-1}$

2. decreases by 99 kg m ${\mathrm{s}}^{-1}$

3. increases by 101 kg m ${\mathrm{s}}^{-1}$

4. decreases by 101 kg m ${\mathrm{s}}^{-1}$

A bullet of mass 5 g is fired from a gun weighing 5.0 kg. If the initial vcelocity of the bullet is 250 m ${\mathrm{s}}^{-1}$. Calculate the velocity with which the gun recoils

1. -0.50 m ${\mathrm{s}}^{-1}$

2. -0.25 m ${\mathrm{s}}^{-1}$

3. +0.05 m ${\mathrm{s}}^{-1}$

4. +0.25 m ${\mathrm{s}}^{-1}$

Consider two spring balances hooked as shown in the figure. We pull them in opposite direction. If the reading shown by A is 1.5 N, the reading shown by B will be

1. 1.5 N

2. 2.5 N

3. 3.0 N

4. zero

Displacement-time graph of an object of mass 2 kg is shown in figure. The force required to move th object for first four seconds is

1. 0

2. 4 N

3. 2 N

4. 8 N

Velocity-time graph of an object of mass 2 kg is shown in figure. The force required to move the object to first four seconds is

1. 0

2. 4 N

3. 2 N

4. 8 N

A car and a motor cycle are moving with the same momentum. When equal retarding forces are applied, the car comes to halt in ${\mathrm{t}}_{1}$ seconds and the motor cycle in ${\mathrm{t}}_{2}$ seconds. If the mass of the car is five times more than the mass of the motor cycle, then

1. ${\mathrm{t}}_{1}={\mathrm{t}}_{2}$

2. ${t}_{1}=5{t}_{2}$

3. ${\mathrm{t}}_{1}=\frac{1}{5}{\mathrm{t}}_{2}$

4. ${\mathrm{t}}_{1}=25{\mathrm{t}}_{2}$

A father has mass 60 kg and the mass of his son is 30 kg. The ratio of the inertia of the father to the inertia of his child is

1. 1:1

2. 1:2

3. 2:1

4. 1:3

A hockey player pushes the ball on the ground. It comes to rest after travelling certain distance because

1. the player stops pushing the ball

2. no balanced force acts on the ball

3. the ball moves only when pushes

4. the opposing force acts on the ball

Two bodies of equal mass (m) moving with equal speed (v) in opposite directions collide. The resultant velocity of the combination is

1. v

2. 2v

3. -v

4. zero

If a constant force acts on a body initially at rest, the distance moved by the body in time t is proportional to

1. t

2. ${t}^{2}$

3. ${t}^{3}$

4. ${t}^{4}$

One newton is equal to

1. ${10}^{5}$ dyne

2. 10 kg m ${\mathrm{s}}^{-2}$

3. ${10}^{3}$ dyne

4. 100 kg m ${\mathrm{s}}^{-2}$

Which is velocity-time graph of a moving particle on which net external force is zero?

A force of 10 N acts on a ball moving on a surface. The force of friction that must act between the surface of the ball and the surface so that the ball keeps on moving with constant velocity over the surface must be

1. zero

2. 100 N

3. 200 N

4. 300 N

A particle of mass 0.3 kg is subjected to a force F=kx with k =15 N/m and x being its distance from the origin. What will be its initial acceleration if it is released from a point 20 cm away from the origin

1. 5 m ${\mathrm{s}}^{-2}$

2. 10 m ${\mathrm{s}}^{-2}$

3. 3 m ${\mathrm{s}}^{-2}$

4. 15 m ${\mathrm{s}}^{-2}$

A ship of mass $3\times {10}^{7}$ kg initially at rest is pulled by a force of $5\times {10}^{4}$ N through a distance of 3 m. Assume that the resistance due to water is negligible, the speed of the ship is

1. 1.5 m ${\mathrm{s}}^{-1}$

2. 60 m ${\mathrm{s}}^{-1}$

3. 0.1 m ${\mathrm{s}}^{-1}$

4. 5 m ${\mathrm{s}}^{-1}$

A body of mass m is at the rest. Another body of same mass moving with velocity v makes head on elastic collision with the first body. After collision the first body starts to move with velocity

1. v

2. 2v

3. remain at rest

4. not predictable

In a rocket, fuel burns at the rate of 1 km ${\mathrm{s}}^{-1}$. This fuel is ejected from the rocket with a velocity of 60 km ${\mathrm{s}}^{-1}$. This exerts a force on the rocket equal to

1. 6000 N

2. 60000 N

3. 60 N

4. 600 N

During a football match, the ball shot towards the goal struck the defender's foot at the speed of 10 m ${\mathrm{s}}^{-1}$ and it bounces back at 20 m ${\mathrm{s}}^{-1}$. If the time of impact was 0.2 sec, and mass of the ball is 1/2 kg, then average force exerted by defender on the ball is

1. 75 N

2. 35 N

3. 50 N

4. 40 N

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