Question:
Explain why some of the leaves may get detached from a tree if we vigorously shake its branch.
Answer:
Some leaves of a tree get detached when we shake its branches vigorously is due to inertia of rest. When the tree moves to and fro, leaves tend to remain in the rest state and resist the change. Due to this, some leaves gets detached and fall down.
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.
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 4.
Fill in the blanks :
The study of motion of a body under the action of a force is called ______.
Q 5.
Do action-reaction forces produce the same magnitude of acceleration ?
Q 6.
Can every force produce motion in every object?
Q 7.
On what factor does inertia of a body depend ?
Q 8.
Explain why a player lowers his hands while catching a cricket ball.
Q 9.
In the above question, which body is damaged more ?
Q 10.
Using second law of motion, derive the relation between force and acceleration.
Q 11.
When a branch of a tree is shaken, some of the fruits may fall down.Why ?
Q 12.
The masses of two objects are 2 kg and 20 kg. Which has greater inertia ?
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.
Can balanced forces change the shape and size of an object?
Q 15.
What is the SI unit of impulse.
Q 16.
It is difficult to balance our body when we accidentally slip on a peel of banana. Explain why?
Q 17.
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 18.
What acceleration is produced by a force of 5 N acting on a body of mass 20 kg ?
Q 19.
A body of mass 25 kg has momentum of 125 kg m/s. What is the velocity of the body?
Q 20.
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 21.
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 22.
Why does a gunman get a jerk on a firing a bullet ?
Q 23.
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 24.
What is the net momentum of gun and bullet system before firing?
Q 25.
Explain what is meant by momentum of a body.Is it a scalar or a vector ? What are its units ?
Q 26.
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 27.
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 28.
What is formula of impulse?
Q 29.
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 30.
Name the unbalanced force that stops a ball rolling on the ground.
Q 31.
State Newton’s third law of motion and principle of conservation of momentum.
Q 32.
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 33.
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 34.
What do you mean by a resultant force?
Q 35.
Name the physical quantity that corresponds to the rate of change of momentum.
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.
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 38.
Why is it advised to tie any luggage kept on the roof of a bus with a rope?
Q 39.
Fill in the blanks :
When a passenger jumps out of moving bus, he falls down. It is due to _______________.
Q 40.
Why does a bicycle slow down when the cyclist stop pedalling?
Q 41.
Which law of motion gives the measure of force?
Q 42.
A machine gun fires 25 g bullets at the rate of 600 bullets per minute with a speed of 200 m/s.Calculate the force required to keep the gun in position.
Q 43.
Can balanced forces move a body at rest ?
Q 44.
What are unbalanced forces ?
Q 45.
What is one newton force ?
Q 46.
State Newton’s second law of motion and establish that F = ma where symbols have their usual meanings.
Q 47.
State Newton's First Law of motion.
Q 48.
Is force required to keep a moving object in motion (yes/no)?
Q 49.
When a carpet is beaten with a stick, dust comes out of it. Explain.
Q 50.
State Newtons second law of motion.
