Question:
An object of mass 5 kg is moving with a velocity 4 m/s. A constant force of 20 N acts on the object. What will be the velocity after 3 s.
Answer:
Give, mass (m) = 5 kg
Initial velocity (u) = 4 m/s
Force (F) = 20 N
Time taken (t) = 3 s
acceleration (a) = ?
final velocity (v) = ?
Since F = ma ⇒ a = F/m
∴ a = 20/5 = 4 m/s2
Using equation v = u + at
v = 4 + 4×3 = 4 + 12 = 16 m/s
Force and Laws of Motion
Q 1.
Are action-reaction forces simultaneous ?
Q 2.
What is the unit of force in c.g.s system?
Q 3.
Fill in the blanks :
The study of motion of a body under the action of a force is called ______.
Q 4.
Can every force produce motion in every object?
Q 5.
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 6.
On what factor does inertia of a body depend ?
Q 7.
Do action-reaction forces produce the same magnitude of acceleration ?
Q 8.
Explain why a player lowers his hands while catching a cricket ball.
Q 9.
When a branch of a tree is shaken, some of the fruits may fall down.Why ?
Q 10.
Using second law of motion, derive the relation between force and acceleration.
Q 11.
What is the SI unit of impulse.
Q 12.
The masses of two objects are 2 kg and 20 kg. Which has greater inertia ?
Q 13.
In the above question, which body is damaged more ?
Q 14.
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 15.
Can balanced forces change the shape and size of an object?
Q 16.
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 17.
It is difficult to balance our body when we accidentally slip on a peel of banana. Explain why?
Q 18.
A body of mass 25 kg has momentum of 125 kg m/s. What is the velocity of the body?
Q 19.
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 20.
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 21.
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 22.
What acceleration is produced by a force of 5 N acting on a body of mass 20 kg ?
Q 23.
What is the net momentum of gun and bullet system before firing?
Q 24.
Why does a gunman get a jerk on a firing a bullet ?
Q 25.
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 26.
The following is the distance-time table of an object in motion :
| Time(s) | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
|---|
|
| Distance (m) | 0 | 1 | 8 | 27 | 64 | 125 | 216 | 343 |
|---|
(a) What conclusion can you draw about the acceleration ? Is it constant ? increasing ? decreasing ?zero ?
(b) What do you infer about the forces acting on the object ?
Q 27.
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 28.
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.
Q 29.
A hockey ball of mass 200 g travelling at 10 m s-1 is struck by a hockey stick so as to return it along its original path with a velocity at 5 m s-1. Calculate the change of momentum occurred in the motion of the hockey ball by the force applied by the hockey stick.
Q 30.
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 31.
What is formula of impulse?
Q 32.
Name the unbalanced force that stops a ball rolling on the ground.
Q 33.
If action is always equal to the reaction, explain how a horse can pull a cart.
Q 34.
Fill in the blanks :
The natural tendency of objects to resist a change in their state of rest or of uniform motion is called ______.
Q 35.
Why does a bicycle slow down when the cyclist stop pedalling?
Q 36.
What is the momentum of a man of mass 75 kg when he walks with a velocity of 2 m/s ?
Q 37.
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 38.
Explain what is meant by momentum of a body.Is it a scalar or a vector ? What are its units ?
Q 39.
State Newton’s third law of motion and principle of conservation of momentum.
Q 40.
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 41.
State why Newton's first law of motion is called law of inertia.
Q 42.
A stone of 1 kg is thrown with a velocity of 20 m s-1 across the frozen surface of a lake and comes to rest after travelling a distance of 50 m. What is the force of friction between the stone and the ice? (Calculate time taken and acceleration also).
Q 43.
When two objects act on each other, does action-reaction force pair cancel out each other?
Q 44.
Write the SI and CGS unit of force.
Q 45.
If the body is found to be accelerated, is the force acting on it balanced or unbalanced?
Q 46.
What do you mean by a resultant force?
Q 47.
Which principle is involved in the working of a jet plane?
Q 48.
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 49.
Can balanced forces move a body at rest ?
Q 50.
Can balanced forces stop a moving body ?
