Question:
Velocity versus time graph of a ball of mass 50 g rolling on a concrete floor is shown in Fig. Calculate the acceleration and frictional force of the floor on the ball.
Answer:
From the graph,we find that
u = 80 m/s,v = 0,t= 8 s
From v = u+at
0 = 80 + a x 8, a = = -10 m/s
As m = 50g= kg = kg
F = ma = (-10)=-0.5 N
Negative sign is for opposing frictional force of the floor on the ball.
Force and Laws of Motion
Q 1.
Can balanced forces change the shape and size of a body ?
Q 2.
What is the total momentum of a bullet and a gun before firing?
Q 3.
What are contact forces? Give examples
Q 4.
A TV set is lying on a table. The TV set experiences a gravitational force (pull) downwards (FW) by the Earth. It also experiences a force on it due to table in contact i.e. (FTable-TV) in upward direction. Do these forces form an action-reaction pair? Do these forces follow Newton's third Law of motion?
Q 5.
A 8000 kg engine pulls a train of 5 wagons, each of 2000 kg, along a horizontal track. If the engine exerts a force of 40000 N and the track offers a friction force of 5000 N, then calculate:
(a) the net accelerating force;
(b) the acceleration of the train; and
(c) the force of wagon 1 on wagon 2.
Q 6.
Is force a scalar or vector quantity?
Q 7.
Is momentum a scalar or vector ?
Q 8.
Explain the use of seat belts in cars.
Q 9.
State Newton’s three laws of motion.
Q 10.
Fill in the blanks :
Which has more inertia of Cricket ball or a rubber ball of the same size? __________
Q 11.
What is the SI unit of momentum?
Q 12.
What is formula of impulse?
Q 13.
Fill in the blanks :
________ is a measure of intertia.
Q 14.
Why is the person hurt less when he falls on a spongy surface?
Q 15.
What would be the force required to produce an acceleration of 2
in a body of mass 12 kg ? What would be the acceleration if the force were doubled ?
Q 16.
Can balanced forces stop a moving body ?
Q 17.
Show that kg-
and N-s represent the same quantity.Which is that quantity ?
Q 18.
Establish relation between inertia and mass.
Q 19.
Give atleast four applications of Newton’s second law of motion.
Q 20.
A truck starts from rest and rolls down a hill with a constant acceleration. It travels a distance of 400 m in 20 s. Find its acceleration. Find the force acting on it if its mass is 7 metric tonnes. (Hint: 1 metric tonne = 1000 kg.)
Q 21.
A man pushes a box of mass 50 kg with a force of 80 N. What will be the acceleration of the box due to this force? What would be the acceleration if the mass were doubled ?
Q 22.
Fill in the blanks :
A cyclist on a levelled road does not come to rest immediately even he stops pedalling. It is due to ______________.
Q 23.
What do you mean by a resultant force?
Q 24.
State Newton's third law of motion.
Q 25.
Do action and reaction act on the same body?
Q 26.
What is the SI unit of impulse.
Q 27.
A bullet of mass 50 g is fired from a gun of mass 6 kg with a velocity of 400 m/s.Calculate the recoil velocity of the gun.
Q 28.
On what factor does inertia of a body depend ?
Q 29.
What is the SI unit of momentum ?
Q 30.
What is the total momentum of the bullet and the gun on firing ?
Q 31.
Are action-reaction forces simultaneous ?
Q 32.
Name the various effects of force.
Q 33.
What is force ? What is inertia ? How is inertia measured ?
Q 34.
Which of the following has more inertia:
(a) a rubber ball and a stone of the same size?
(b) A bicycle and a train?
(c) A five-rupee coin and a one-rupee coin?
Q 35.
What a force can do?
Q 36.
Why is it advised to tie any luggage kept on the roof of a bus with a rope?
Q 37.
Is Newton's second law of motion is consistent with the first law? How?
Q 38.
State Law of conservation of momentum.
Q 39.
Define force of friction.
Q 40.
How is force related to momentum of a body?
Q 41.
A certain force exerted for 1 -2 s raises the speed of an object from 1.8 m/s to 4.2 m/s. Later,the same force is applied for 2 second. How much does the speed change in 2 s ?
Q 42.
Which would require a greater force : accelerating a 2 kg mass at 5
or a 4 kg mass at 2
?
Q 43.
For how long should a force of 100 N act on a body of mass 20 kg so that it acquires a velocity of 100 m/s ?
Q 44.
A hockey ball of mass 200 g travelling at 10 m/s is struck by a hockey stick so as to return it along its original path with a velocity of 5 m/s.Calculate the change in momentum of the hockey ball by the force applied by the hockey stick.
Q 45.
A bullet of mass 10 g travelling horizontally with a velocity of 150
strikes a block and comes to rest in 0.03 s. Calculate the distance of penetration of the bullet into the block.Also, calculate the magnitude of the force exerted by the wooden block on the bullet.
Q 46.
Derive the unit of force using the second law of motion. A force of 5 N produces an acceleration of
on a mass
and an acceleration of 24
on a mass
.What acceleration would the same force provide if both the masses are tied together ?
Q 47.
State the law of conservation of linear momentum.
Q 48.
Explain what is meant by momentum of a body.Is it a scalar or a vector ? What are its units ?
Q 49.
State Newton’s third law of motion and principle of conservation of momentum.
Q 50.
A force of 5 N changes the velocity of a body from 10
to 20
in 5 sec.How much force is required to bring about the same change in 2 sec ?
