CBSE Questions for Class 9 Physics Force And Laws Of Motion Quiz 11 - MCQExams.com

A stone is tied to the middle of a string and suspended from one end as shown in the given figure. Here S is the stone and O is the point of suspension. If we increase the pull at P gradually, the string will break
366248_45465af5408547d59249d4a4ea640875.png
  • below the stone
  • at the point P itself
  • above the stone
  • nothing can be decided
Two solid rubber balls A and B having masses 200 g and 400 g respectively are moving in opposite directions with velocity of A equal to 0.3 ms$$^{-1}$$. After collision the two balls come to rest then velocity of B is :
  • -0.15 ms$$^{-1}$$
  • 0.15 ms$$^{-1}$$
  • 1.5 ms$$^{-1}$$
  • none of these
A book is at rest on a table. What is the "reaction" force according to Newton's third law to the gravitational force by the earth on the book?
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  • the normal force exerted by the table on the book
  • the normal force exerted by the table on the ground
  • the normal force exerted by the ground on the table
  • the gravitational force exerted on the earth by the book.
Statement 1: When a man is standing on a stationary horizontal surface, the normal force exerted by the ground on him is equal and opposite to his weight.
Statement 2: According to Newton's $$3^{ rd }$$ law , every action has an equal and opposite reaction.
  • Statement 1 - is true, statement- 2 is true and statement-2 is correct explanation for statement-1
  • Statement 1 - is true, statement- 2 is true and statement-2 is NOT the correct explanation for statement-1
  • Statement 1 - is true, statement- 2 is false
  • Statement 1 - is false, statement- 2 is true
A bullet of mass $$20g$$ and moving with a velocity of $$200m/s$$ strikes a heap of sand and comes to rest after penetrating $$3cm$$ inside it. The force exerted by the sand on the bullet will be:
  • $$11.2\times { 10 }^{ 8 }dyne$$
  • $$15.7\times { 10 }^{ 8 }dyne$$
  • $$13.3\times { 10 }^{ 8 }dyne$$
  • $$18.6\times{ 10 }^{ 8 }dyne$$
A heavy uniform bar is being carried by two men on their shoulders. The weight of the bar is $$w$$. What is the work done by gravity?
  • $$w/4$$
  • $$w/2$$
  • $$w$$
  • $$0$$
A $$20 g$$ bullet passes through a plate of mass $$1 kg$$ and finally comes to rest inside another plate of mass $$2980 g$$. It makes the plates move from rest to same velocity. The percentage loss in velocity of bullet between the plate is:
136678_a7c696f9961e4a1b9066628a11d6ec3a.png
  • $$0$$
  • $$50$$%
  • $$75$$%
  • $$25$$%
A rocket is moving at a constant speed in space by burning its fuel and ejecting out the burnt gases through a nozzle. Is there any force acting on the rocket? If yes, how much?
  • Yes, equal to rate of change in momentum
  • No
  • Yes, equal to rate of change in velocity
  • Yes, equal to change in mass 
A force of $$5N$$ acts horizontally on a body of weight $$9.8N$$. What is the acceleration produced (in $${ ms }^{ -2 }$$)?
  • $$0.51$$
  • $$1.46$$
  • $$49.00$$
  • $$5.00$$
A body acted upon by a force $$F$$ has an acceleration $$A$$. When it is acted upon by two forces each of magnitude $$F$$ perpendicular to each other, its acceleration will be:
  • $$2A$$
  • $$A$$
  • $$A \sqrt 2$$
  • $$\sqrt 2$$
Consider the following statements:
(a) No net force acts on a rain drop falling vertically with a constant speed.
(b) If net force acting on the body is zero, momentum of the body remains constant.
(c) Particle of different masses falls with different acceleration on earth.
(d) It is easier to start motion in a heavier body than a lighter body.
Which of the above statements are correct?
  • (b) and (c)
  • (a) and (b)
  • (a), (b) and (d)
  • All of the above
The speed-times relation of a car whose weight is $$1500kg$$ as shown in the given graph. How much breaking force has been applied at the end of $$7$$sec, to stop the car in $$2$$ sec?
197769_4e82014788984be2aebcb2e03548b20a.png
  • $$2000N$$
  • $$1200N$$
  • $$4800N$$
  • $$8400N$$
  • $$9000N$$
Two bodies of masses $$m$$ and $$3m$$, moving with velocities $$3v$$ and $$v$$ respectively along same direction, collide with each other. After collision they stick together and move with a velocity $$V$$ in the same direction. Then:
  • $$\displaystyle V= v$$
  • $$\displaystyle V=\frac {3}{2}v$$
  • $$\displaystyle V=2v$$
  • $$\displaystyle V = \frac {4}{3}v$$
When a net force acts on an object, the object will be accelerated in the direction of the force with an acceleration proportional to
  • the force on the object
  • the velocity of the object
  • the mass of the object
  • the inertia of the object
How can Newton's first law of motion be obtained from the second law of motion?
  • When net force is zero.
  • When net force is positive.
  • When moving with constant velocity.
  • When velocity is zero.
A large truck and a car, both moving with a velocity of magnitude $$v$$, have a head-on collision. If the collision lasts for $$1\ s$$. Which vehicle experiences greater acceleration?
  • Car
  • Truck
  • Both have equal acceleration
  • Cannot say
A large truck and a car, both moving with a velocity of magnitude $$v$$, have a head-on collision. If the collision lasts for $$1\ s$$ which vehicle experiences greater force of impact?
  • Truck
  • Car
  • Both experience equal and opposite force
  • Data insufficient
Suppose you push a spring with a force $$F_1$$ as shown in figure, the spring also pushes up on your hand with a force $$F_2$$. What is the relationship between $$F_1$$ and $$F_2$$?

246357_d7904ef3f2b546ecb55f7a2afc45a804.png
  • $$F_1 > F_2$$
  • $$F_1 = 2F_2$$
  • $$F_1 < F_2$$
  • $$F_1 = F_2$$
A bullet of mass $$10\ g$$ moving with the velocity of $$1.5\ ms^{-1}$$ hits a thick wooden plank of mass $$90\ g$$. The plank is initially at rest, but when it gets hit by the bullet, the bullet remains in the plank, and both move with a certain speed. Calculate the speed with which the plank containing the bullet moves?
  • $$0.15\ ms^{-1}$$
  • $$0.5\ ms^{-1}$$
  • $$1.5\ ms^{-1}$$
  • $$2\ ms^{-1}$$
Two small glass spheres of masses 10 g and 20 g are moving in a straight line in the same direction with velocities of $$3 ms^{-1}$$ and $$2 ms^{-1}$$ respectively. They collide with each other. After collision, glass sphere of mass 10 g moves with a velocity of $$2.5 ms^{-1}$$. Find the velocity of the second ball after collision.
  • $$2.25 ms^{-1}$$
  • $$5.5 ms^{-1}$$
  • $$2.75 ms^{-1}$$
  • $$7.5 ms^{-1}$$
The earth and the moon are attracted to each other by gravitational force. Is the force with which the Earth attracts the Moon greater, smaller or the same as the force with which the Moon attracts the Earth?
  • Same and opposite
  • Greater
  • Smaller
  • Data insufficient
Student A and student B sit in identical office chairs facing each other, as shown in figure. Student A is heavier than student B. Student A suddenly pushes with his feet. Which of the following occurs?

246368_77f1b741c3514051a42d6f33d9c1cf2e.png
  • Neither student applies a force on each other
  • A exerts a force that is applied to B, but A experiences no force
  • Each student applies a force to the other, but A exerts the larger force
  • The students exert the same amount of force on each other
Student A and student B sit in identical office chairs facing each other, as shown in figure. Student A is heavier than student B. Student A suddenly pushes student B with his feet. Suppose $$v_A$$ and $$v_B$$ are the velocities of student A and student B respectively, then

246375_ddb67901c7bb4d61860576a143657b14.png
  • $$v_A > v_B, v_A$$ is leftward and $$v_B$$ is rightward
  • $$v_A < v_B, v_A$$ is leftward and $$v_B$$ is rightward
  • $$v_A = v_B, v_A$$ is leftward and $$v_B$$ is rightward
  • $$v_A > v_B, v_A$$ and $$v_B$$ both are rightward
Two solid rubber balls, $$A$$ and $$B$$ having masses $$200 \ g$$ and $$400 \ g$$ respectively are moving in opposite directions with velocity of $$A$$ equal to $$0.3\:m/s$$. After collision the two balls come to rest, then the velocity of $$B$$ is-
  • $$0.15\:m/s$$
  • $$1.5\:m/s$$
  • $$-0.15\:m/s$$
  • None of the above
A space-craft of mass $$M$$ moves with a velocity $$V$$ and suddenly explodes into two pieces. If a part of mass $$m$$ becomes stationary, then the velocity of another part will be :
  • $$\dfrac{MV}{(M - m)}$$
  • $$\dfrac{MV}{(M + m)}$$
  • $$\dfrac{mV}{M - m)}$$
  • $$\dfrac{mV}{M + m)}$$
If a constant external force starts acting on a moving particle, then:
  • The line of motion of the particle will keep changing
  • The speed of the particle will keep changing
  • The particle will keep moving
  • All of the above are correct.
A bullet of mass m = 50 gm strikes a bag of mass M = 5 kg hanging from a fixed point, with a horizontal velocity $$\bar{V}_p$$. If bullet sticks to the sand bag then just after collision the ratio of final & initial kinetic energy of the bullet is approximately :
  • $$10^{-2}$$
  • $$10^{-3}$$
  • $$10^{-6}$$
  • $$10^{-4}$$
In which of the following cases the net force is not equal to zero?
  • A kite skillfully held stationary in the sky
  • A ball falling freely from a height
  • A helicopter hovering above the ground
  • A cork floating on the surface of water
A soldier with a machine gun, falling from an airplane gets detached from his parachute. He is able to resist the downward acceleration if the shoots 40 bullets a second at the speed of 500 m/s. If the mass of a bullet is 49 gm, what is the mass of the man with the gun ? Ignore resistance due to air and assume the acceleration due to gravity g = 9.8 $$m/s^2$$.
  • 60 kg
  • 75 kg
  • 100 kg
  • 125 kg
A massive ball moving with speed v collides head-on with a tiny ball at rest having a very small mass as compared to the first ball. If the collision is elastic, then immediately after the impact, the second ball will move with a speed approximately equal to 
  • v
  • 2v
  • v/2
  • $$\infty$$
0:0:1


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