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

Swimming is possible on account of :-
  • First law of motion
  • Second law of motion
  • Third law of motion
  • Newton's law of motion
The action and reaction force referred to in the third law
  • must act on the same object
  • must act on different object
  • may act on different object
  • act in the same direction
An object of mass 10 kg moves at a constant speed of 10m/s. A constant force that acts for 4 sec on the object gives it a speed of 2m/s in opposite direction. The force acting on the object is:
  • -3N
  • -30N
  • 3N
  • 30N
A ball of mass $$0.2 \ kg$$ is thrown vertically upwards by applying a force by hand. If the hand moves $$0.2 \ m$$ while applying the force and the ball goes upto $$2 \ m$$ height further, find the magnitude of force applied by the hand. Consider $$g =10$$ $${ ms }^{ -2 }$$.
  • $$20 \ N$$ 
  • $$22 \ N$$ 
  • $$4 \ N$$ 
  • $$16 \ N$$ 
Assertion (A): According to Newton’s third law sum of action and reaction is not equal to zero 
Reason (R) : The forces action and reaction acts on different bodies.
  • A and R are correct and R is the correct explanation of A
  • A and R are correct and R is not the correct explanation A
  • A is true and R is false
  • A is false and R is true
A man is standing on a spring platform. The reading of spring balance is 60 kg wt. If the man jumps outside the platform, then the reading of the spring balance:
  • remains the same
  • decreases
  • increases
  • first increases and then decreases to zero
When two identical balls are moving with equal speeds in opposite directions, which of the following is true for the system of two bodies?
  • Momentum is zero, kinetic energy is zero
  • Momentum is not zero, kinetic energy is zero
  • Momentum is zero, kinetic energy not zero
  • Momentum is not zero, kinetic energy is not zero
A parachutist along with the parachute has a mass of 75 kg. He jumps from a large height and is coming down with a uniform velocity with the parachute fully opened. The magnitude of force due to the air resistance is: ( take g$$={10m/s}^{ 2 }$$).
  • $$zero$$
  • $$< 750 N$$
  • $$> 750 N$$
  • $$750N$$
When you are holding a ball in your hand, the reaction force to the force of gravity on the ball is, the force exerted by the:
  • ball on the earth.
  • ball on the hand.
  • hand on the ball.
  • earth on the ball.
Inside a railway car a plumb bob (a heavy mass suspended by a thread) is suspended from the roof and a helium filled balloon is tied by a string to the floor of the car. When the railway car accelerates to the right, then
  • Both the plumb bob and balloon move to the left
  • Both the plumb bob and balloon move to the right
  • Plumb bob moves to the left and the balloon moves to the right
  • Plumb bob moves to the right and the balloon moves to the left
A father and his seven year old son are facing each other on ice skates (assume no friction with the ground). With their hands, they push off against one another. Regarding the forces that act on them as a result of this and the accelerations they experience. Which of the following statements is correct?
  • Father exerts more force on the son and experiences less acceleration.
  • Son exerts less force on the father and experiences more acceleration.
  • Father exerts as much force on the son as the son exerts on the father, but the father experiences less acceleration.
  • Father exerts as much force on the son as the son exerts on the father, but the father experiences more acceleration.
Two astronauts A and B off mass $$m_a$$ and $$m_b$$ are in space. A pushes B with some force. ($$m_a =m_b$$)
  • acceleration of A is greater than that of B
  • acceleration of A is less than that of B
  • neither is accelerated
  • their accelerations are equal in magnitude but opposite in direction
A body of mass $$2 \ kg$$ moving on a horizontal surface with an initial velocity of $$4 \ ms^{-1}$$, comes to rest after $$2 \ s$$. If one wants to keep this body moving on the same surface with a velocity of $$4ms^{-1}$$, the force required is:
  • zero
  • $$2 \ N$$
  • $$4 \ N$$
  • $$8 \ N$$
A person weighing 60 kg in a small boat of mass 140 kg that is at rest, throws a 5 kg stone in the horizontal direction with a velocity of $$14ms^{-1}$$ . The magnitude of velocity of the boat immediately after the throw is:
  • $$1.2 ms^{-1}$$
  • $$0.5 ms^{-1}$$
  • $$0.35 ms^{-1}$$
  • $$0.65 ms^{-1}$$
A bullet of mass $$10\ g$$ moving with a horizontal velocity $$100\   m/s$$ passes through a wooden block of mass $$100\ g$$. The block is resting on a smooth horizontal floor. After passing through the block the velocity of the bullet is $$10\ m/s$$. The velocity of the emerging bullet with respect to the block is:
  • $$10\  m/s$$
  • $$9 \ m/s$$
  • $$1 \ m/s$$
  • $$5\  m/s$$
A man and a cart move towards each other. The man weighs 64 kg and the cart 32 kg. The velocity of the man is 5.4 km/hr and that of the cart is 1.8km/hr. When the man approaches the cart, he jumps on to it. The velocity of the cart carrying the man will be:
  • 30 km/hr
  • 3 km/hr
  • 1.8 km/ hr
  • zero
A $$60 \ kg$$ boy lying on a surface of negligible friction throws a stone of mass $$1 \ kg$$ horizontally with a speed of $$12 \ m/s$$ away from him. With what kinetic energy does he move back due to result of this action?
  • $$2.4$$ $$J$$
  • $$7.2$$ $$J$$
  • $$1.2$$ $$J$$
  • $$36$$ $$J$$
When a gun of mass $$M$$ fires a bullet of mass $$m$$, the total energy released in the explosion is found to be $$E$$. The kinetic energy of the bullet is:
  • $$\dfrac{EM}{(M+m)}$$
  • $$\dfrac{Em}{(M+m)}$$
  • $$\dfrac{E(M+m)}{M}$$
  • $$\dfrac{E(M+m)}{m}$$
If a net force $$F$$ applied to an object of mass $$m$$ will produce an acceleration of $$a$$, what is the mass of a second object which accelerates at $$5a$$ when acted upon by a net force of $$2F$$?
  • $$\dfrac{2}{5}m$$
  • $$2m$$
  • $$\dfrac{5}{2} m$$
  • $$5m$$
A man stands on the surface of the earth. The number of action reaction pairs that can be seen here is/are 
  • 1
  • 2
  • 4
  • 5
A horizontal force $$F $$ produces an acceleration of  $$6 \ m/ s^{2}$$ on a block resting on a smooth horizontal surface. The same force produces an acceleration of $$3\ m/ s^{2}$$ on a second block resting on a smooth horizontal surface. If the two blocks are tied together and the same force acts, the acceleration produced will be:
  • $$9\ m/ s^{2}$$
  • $$2\ m/ s^{2}$$
  • $$4\ m/ s^{2}$$
  • $$\dfrac{1}{2}\ m/ s^{2}$$
A $$10\ N$$ force applied on a body produces in it an acceleration of $$2\ m{ s }^{ -2 }$$. The mass of the body is 
  • $$2\ kg$$
  • $$5\ kg$$
  • $$10\ kg$$
  • $$20\ kg$$
A trolley of mass $$60 kg$$ moves on a smooth horizontal surface and has kinetic energy $$120 J$$.A mass of $$40 kg$$ is lowered vertically on to the trolley. The total kinetic energy of the system after lowering the mass is:
  • $$60 J$$
  • $$72 J$$
  • $$120 J$$
  • $$144 J$$
A block weighing $$30 \ N$$ is on a smooth horizontal surface and it is accelerated in the horizontal direction at a rate of $${4 \ m/s}^{ 2 }$$ by a force. The net force in horizontal direction acting on the block is (g $$={ 10  m/s }^{ 2 }$$ ):
  • 12 N
  • 120 N
  • 50 N
  • 10 N
 A boy weighing 50 kg throws a stone of mass 10 kg horizontally with a velocity of $$8 ms^{-1}$$. With what velocity does he move after throwing?
  • $$ -1.6 ms^{-1}$$
  • $$-16 ms^{-1}$$
  • $$ -160 ms^{-1}$$
  • $$-1.9 ms^{-1}$$
A gun fires a bullet of mass 50 g with a velocity of mass $$130$$ ms$$^{-1}$$. Because of this, the gun is pushed back with a velocity of $$1$$ ms$$^{-1}$$. The mass of the gun is :
  • 15 kg
  • 30 kg
  • 6.5 kg
  • 20 kg
The net force on a rocket with a weight of $$1.5\times 10^{4}N$$ is $$2.4 \times 10^{4}N$$. About how much time is needed to increase the rocket's speed from $$12 m/s$$ to $$36 m/s$$ near the surface of the Earth at take off? (Take $$g=10m/s^2$$)
  • $$15 s$$
  • $$0.78 s$$
  • $$1.5 s$$
  • $$3.8 s$$
 A bullet of mass 20 gm is fired from a rifle of mass 20 kg with a muzzle velocity of $$200\ ms^{-1}$$. Find the velocity of recoil of the rifle.
  • $$0.4ms^{-1}$$
  • $$0.5ms^{-1}$$
  • $$0.2ms^{-1}$$
  • $$0.3ms^{-1}$$
 A bullet is fired from a gun with a velocity 600 m/s. The recoil velocity of the gun is 3 m/s. What is the ratio of the mass of the gun and bullet ? 
  • 100:1
  • 400:1
  • 200:1
  • 300:2
 A bullet of mass 125 gm leaves a rifle with a velocity of $$500ms^{-1}$$. The rifle recoils with a velocity of $$5ms^{-1}$$. Find the mass of the rifle.
  • 100 kg
  • 12.5 kg
  • 1.25 kg
  • 125 kg
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