Question:
Identify the action and reaction forces in the following cases:
(a) A television (TV) lying on a table
(b) Pushing a wall with your hand
(c) Firing a bullet from a gun.
(d) Walking of a person on a ground.
Answer:
(a) A TV lying on a table: TV is interacting with table surface. Applying Newton's third law of motion, action force acts on table due to TV (FTV-Table) and a reaction force acts on TV by the table i.e. (FTable-TV). Both these forces are equal in magnitude but in opposite directions.
⇒ FTable-TV = - FTV-Table
(b) Pushing a wall with your hand: When you pushes a wall, you exert a force (action) on the wall. Similarly, the wall exerts a (reaction) force on your hands in contact with the wall. According to Newton;s third law of motion, both these forces form action-reaction pair and act on different bodies. Both are equal in magnitude but opposite in direction.
(c) Firing a bullet from a gun: When a gun fires a bullet, a force is exerted (action) on a bullet and the gun experiences an equal recoil (reaction) force in opposite direction.
(d) Walking of a person on a ground: When a person pushes the ground (action) backwards by his foot, the ground also exerts an equal force (reaction) on the his foot in forward direction.
Force and Laws of Motion
Q 1.
While driving on a highway, an insect strikes on the car windshield and splatters. Which experiences greater impact (force): an insect or the windshield?
Q 2.
Are action-reaction forces simultaneous ?
Q 3.
What is the unit of force in c.g.s system?
Q 4.
Do action-reaction forces produce the same magnitude of acceleration ?
Q 5.
Fill in the blanks :
The study of motion of a body under the action of a force is called ______.
Q 6.
On what factor does inertia of a body depend ?
Q 7.
Can every force produce motion in every object?
Q 8.
Explain why a player lowers his hands while catching a cricket ball.
Q 9.
Can balanced forces change the shape and size of an object?
Q 10.
In the above question, which body is damaged more ?
Q 11.
Using second law of motion, derive the relation between force and acceleration.
Q 12.
When a branch of a tree is shaken, some of the fruits may fall down.Why ?
Q 13.
An object of mass 1 kg travelling in a straight line with a velocity of 10 m/s collides with, and sticks to, a stationary wooden block of mass 5 kg. Then they both move off together in the
same straight line. Calculate the total momentum just before the impact and just after the impact. Also, calculate the velocity of the combined object.
Q 14.
The masses of two objects are 2 kg and 20 kg. Which has greater inertia ?
Q 15.
A car weighs 1500 kg.Its speed time graph is shown in Fig. Calculate the force required at the end of 5 seconds to bring the car to a stop within one second.
Q 16.
What acceleration is produced by a force of 5 N acting on a body of mass 20 kg ?
Q 17.
It is difficult to balance our body when we accidentally slip on a peel of banana. Explain why?
Q 18.
What is the SI unit of impulse.
Q 19.
A body of mass 25 kg has momentum of 125 kg m/s. What is the velocity of the body?
Q 20.
What is formula of impulse?
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.
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 23.
An object experiences a net zero external unbalanced force.Is it possible for the object to be travelling with a non-zero velocity ? If yes,state the conditions that must be placed on the magnitude and direction of the velocity.If no,provide a reason.
Q 24.
A hammer of mass 500 g, moving at 50 m/s, strikes a nail. The nail stops the hammer in a very short time of 0.01 s. What is the force of the nail on the hammer ?
Q 25.
Why does a gunman get a jerk on a firing a bullet ?
Q 26.
State Newton's First Law of motion.
Q 27.
Name the unbalanced force that stops a ball rolling on the ground.
Q 28.
From a rifle of mass 4 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.
Q 29.
What do you mean by a resultant force?
Q 30.
What is the net momentum of gun and bullet system before firing?
Q 31.
What is the momentum of a man of mass 75 kg when he walks with a velocity of 2 m/s ?
Q 32.
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 33.
A hammer of mass 500 g,moving at 50 m/s,strikes a nail.The nail stops the hammer in a very short time of 0.01 s.What is the force of the nail on the hammer ?
Q 34.
Explain what is meant by momentum of a body.Is it a scalar or a vector ? What are its units ?
Q 35.
Establish relation between inertia and mass.
Q 36.
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 ?
Q 37.
Why is it advised to tie any luggage kept on the roof of a bus with a rope?
Q 38.
If action is always equal to the reaction, explain how a horse can pull a cart.
Q 39.
Why does a bicycle slow down when the cyclist stop pedalling?
Q 40.
Define 1 Newton force.
Q 41.
Define inertia. How it is measured?
Q 42.
Suppose you were pushing on a heavy bucket of stones with 100 N of force and it did not move. How many newtons of force would be balancing the force that you were applying?
Q 43.
What did Galileo conclude on the basis of his experiments on the motion of objects?
Q 44.
A feather of mass 10 g is dropped from a height.It is found to fall down with a constant velocity.What is the net force acting on it ?
Q 45.
Two objects of masses 100 g and 200 g are moving along the same line in the same direction with velocities of 2 m/s and 1 m/s,respectively.They collide and after the collision, the first object moves at a velocity of 1.67 m/s in the same direction.Determine the velocity of the second object
Q 46.
What is the momentum of an object of mass m,moving with a velocity v ?(a)
(b)
(c)
(d) mv
Q 47.
What are unbalanced forces ?
Q 48.
Derive the relation F = ma,where the symbols have their usual meanings.
Q 49.
State Newton’s third law of motion and principle of conservation of momentum.
Q 50.
State Newton’s second law of motion and establish that F = ma where symbols have their usual meanings.
