CBSE Questions for Class 9 Physics Force And Laws Of Motion Quiz 12 - MCQExams.com

A body $$A$$ of mass $$150 \ kg$$, travelling at $$20 \ m/s$$ collides with a body $$B$$ of mass $$100 \ kg$$ travelling at $$10 \ m/s$$ in the same direction. After collision the velocity of $$A$$ becomes $$15 \ m/s$$. What is the magnitude of velocity of $$B$$ after the collision?
  • $$22.5 \ m/s$$
  • $$17.5 \ m/s$$
  • $$5 \ m/s$$
  • $$12.5 \ m/s$$
What is the recoil velocity of the gun of mass $$8$$ kg when a bullet of mass $$10$$ g is fired from it with a velocity of $$400$$ m/s ?
  • $$5$$ m/s
  • $$2$$ m/s
  • $$50$$ m/s
  • $$0.5$$ m/s
Equal force F acts on isolated bodies X and Y as shown in figure. The mass of Y is three times that of X. The magnitude of the acceleration of X is ..........
315198_6a82863bdac24d4ba475b6259ca31723.png
  • Three times that of Y
  • 1/3 that of Y
  • Nine times that of Y
  • 1/9 that of Y
The 35 kilogram girl is standing on a 20 kilogram wagon and jumps off, giving the wagon a kick that sends it off at 3.8 meters per second. How fast is the girl moving?
  • 1.2 m/s
  • 3 m/s
  • 4 m/s
  • 2.2 m/s
A boy sitting on the top most berth in the compartment of a train which is just going to stop on the railway station, drops an apple aiming at the open hand of his brother situated vertically below his hands at a distance of about $$2 \ m$$. The apple will fall
  • In the hand of his brother
  • Slightly away from the hand of his brother in the direction of the motion of the train.
  • Slightly away from the hands of his brother in the direction opposite to the direction of the motion of the train.
  • None of these
A man fires a bullet of mass $$200\ g$$ at a speed of $$5\ m/s$$. The gun is of mass $$1\ kg$$. The velocity with which the gun will recoil backward is:
  • $$3\ ms^{-1}$$
  • $$2\ ms^{-1}$$
  • $$1\ ms^{-1}$$
  • $$0.01\ ms^{-1}$$
Four forces are acting on a body. If the body doesn't change its position or shape, the forces :
  • Must be of equal magnitude
  • Must be parallel & opposite
  • Must add up to zero when taken as vectors
  • Must be in a single line
A boat at rest has two persons of unequal weights seated at either end. If they walk across the boat and interchange their positions,
  • The boat will move in the direction of walking of the lighter person
  • The boat will move in the direction of walking of the heavier person
  • The boat will not move at all
  • The boat will oscillate about a mean position and stop once the persons have moved to the new positions
  • None of these
Why is it advised to tie any luggage kept on the roof of a bus with a rope?
  • While the bus is moving, luggage tends to remain in inertia of motion state
  • When the bus stops, the luggage tends to resist the change and due to inertia of motion it move forward and may fall off
  • Both a and b are true
  • None of them is True
Consider two spring balances hooked as shown in the figure. We pull them in opposite directions. If the reading shown by A is 1.5 N, the reading shown by B will be :
366258_8d9d182655724f3b8855a532bf212e63.png
  • $$1.5N$$
  • $$2.5N$$
  • $$3.0N$$
  • $$zero$$
According to Newton's Third Law of Motion, action and reaction are equal and opposite. The resultant force is not zero because:
  • They act at different times
  • They act on different bodies
  • Their lines of action are different
  • They act on the same body
A driver first accelerates his car at a rate of $$\displaystyle 1.8{ m }/{ { s }^{ 2 } }$$ and then at a rate of $$\displaystyle 1.2{ m }/{ { s }^{ 2 } }$$. The ratio of the forces exerted by the engines respectively will be equal to
  • 2 : 3
  • 1 : 2
  • 2 : 1
  • 3 : 2
Every action has reaction. These action-reaction are 
  • Equal, opposite and acting on the same body
  • Equal, in the same direction and acting on same body
  • Equal, opposite and acting on different bodies
  • Equal, in same direction and acting on different bodies.
A bullet of mass 0.01 kg is fired from a gun weighing 5.0 kg. If the initial speed of the bullet is 250 m/s, calculate the speed with which the gun recoils.
  • -0.50 m/s
  • - 0.25 m/s
  • + 0.05 m/s
  • +0.25 m/s
Physical independence of force is a consequence of _____.
  • first law of motion
  • second law of motion
  • third law of motion
  • all ofthese laws
The mass of balloon and its contents is M. It is descending with an acceleration a. By how much the mass should be decreased, keeping the volume constant, so that the balloon starts ascending with the same acceleration? 
  • $$\displaystyle \frac { a }{ a+g } M$$
  • $$\displaystyle \frac { g }{ a+g } M$$
  • $$\displaystyle \frac { 2a }{ a+g } M$$
  • $$\displaystyle \frac { 2g }{ a+g } M$$
What is the momentum of a 100000 kg truck whose velocity is 2 m/s?
  • $$2 \times 10^5 kg m/s$$
  • $$1 \times 10^5 kg m/s$$
  • 4 kg m/s
  • none of these
A ball A of mass 2.5kg moving at 5 m/s collides with an identical ball B at rest. A stops and B starts moving. What is the magnitude of velocity of B after the collision?
  • 5 m/s
  • 12.5 m/s
  • 2.5 m/s
  • 10 m/s
The rocket engine lifts a rocket from the earth, because hot gases:
  • push it against the air with very high velocity
  • push it against the earth with very high velocity
  • heat up the air which lifts the rocket with very high velocity
  • react against rocket and push it up with very high velocity
Two bodies of equal masses (M) moving with equal velocities (V) in opposite direction collide. Resultant velocity of the combination:
  • $$V$$
  • $$Va$$
  • $$-V$$
  • Zero
Mark the incorrect option:
  • Balanced forces cannot set any stationary body into motion
  • Balanced forces cannot change the speed of a moving body
  • Balanced forces change the shape and size of a soft body
  • None
If the momentum of a body is doubled, the kinetic energy is
  • Halved
  • Unchanged
  • Doubled
  • Becomes 4 times
An $$80\;\text{kg}$$ person is parachuting and is experiencing a downward acceleration of $$2.8\;\text{m/s}^2$$. The mass of the parachute is $$5\;\text{kg}$$. The net force on the system (parachute+man) is (Take $$\text{g=9.8 m/s}^2$$):
  • $$238\;N$$
  • $$675\;N$$
  • $$456\;N$$
  • $$925\;N$$
The force applied on a body depends on the area over which it acts 
  • True
  • False
Mark the correct statement.
  • Acceleration produced in a body $$\propto$$ force applied on the body
  • Acceleration produced in a body $$\propto \dfrac {1}{\text {Mass of the body}}$$
  • Both
  • None
A body moves with uniform speed along a straight line. So, it is acted upon by:
  • Unbalanced force
  • Balanced force
  • No net external force
  • None of these
From a rifle of mass $$40\ kg$$, a bullet of mass $$50\ g$$ is fired with an initial velocity of $$35\ m/s$$. Calculate the initial recoil velocity of the rifle:
  • $$0.04375\ m/s$$
  • $$0.4375\ m/s$$
  • $$0.2235\ m/s$$
  • $$0.00223\ m/s$$
Two tugboats are moving a barge. Tugboat A exerts a force of $$3000$$ newtons on the barge. Tugboat B exerts a force of $$5000$$ newtons in the same direction. What is the combined force on the barge?
  • $$2000\ N$$
  • $$8000\ N$$
  • $$3000\ N$$
  • $$5000\ N$$
X and Y are two objects with masses $$100\ kg$$ and $$75\ kg$$ respectively, then :
  • Both will have the same inertia
  • Y will have more inertia
  • X will have more inertia
  • Can not be compared
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 a stop because
  • The batsman did not hit the ball hard enough
  • Velocity is proportional to the force exerted on the ball
  • There is a force on the ball opposing the motion
  • There is no unbalanced force on the ball, so the ball would want to come to rest
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