Question:
Explain why a player lowers his hands while catching a cricket ball.
Answer:
Refer to Art.2.13,Page 89.
Force and Laws of Motion
Q 1.
Are action-reaction forces simultaneous ?
Q 2.
On what factor does inertia of a body depend ?
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.
Can every force produce motion in every object?
Q 6.
It is difficult to balance our body when we accidentally slip on a peel of banana. Explain why?
Q 7.
What is the SI unit of impulse.
Q 8.
Explain why a player lowers his hands while catching a cricket ball.
Q 9.
Fill in the blanks :
The study of motion of a body under the action of a force is called ______.
Q 10.
The masses of two objects are 2 kg and 20 kg. Which has greater inertia ?
Q 11.
A body of mass 25 kg has momentum of 125 kg m/s. What is the velocity of the body?
Q 12.
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 13.
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 14.
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 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.
When a branch of a tree is shaken, some of the fruits may fall down.Why ?
Q 17.
Using second law of motion, derive the relation between force and acceleration.
Q 18.
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 19.
Can balanced forces change the shape and size of an object?
Q 20.
What is the net momentum of gun and bullet system before firing?
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.
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 23.
In the above question, which body is damaged more ?
Q 24.
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 25.
Why is the person hurt less when he falls on a spongy surface?
Q 26.
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 27.
Fill in the blanks :
When a bus starts suddenly, the bus passengers standing in the bus tend to fall backwards. It is due to _______________.
Q 28.
Fill in the blanks :
________ is the tendency of an object to resist a change in motion.
Q 29.
Why does a gunman get a jerk on a firing a bullet ?
Q 30.
Discuss briefly Galileo's ideas about motion.
Q 31.
Honey and Sunny are two friends.Both are financially well off.Honey is fond of driving an SUV while Sunny enjoys driving Tata Nano.Honey explains to Sunny the risks of driving a light vehicle and Sunny explains to Honey the cost factor.
Read the above passage and answer the following questions :
(i) With whom do you agree,with Honey or with Sunny?
(ii) Explain, why?
(iii) Which values of life do you learn from this discussion?
Q 32.
Fill in the blanks :
It is dangerous to jump out of a moving bus because due to _________ one falls forward.
Q 33.
What is formula of impulse?
Q 34.
A body of mass 1 kg is kept at rest.A constant force of 6-0 N starts acting on it.Find the time taken by the body to move through a distance of 12 m.
Q 35.
What is the other name for Newton's first law of motion ?
Q 36.
What acceleration is produced by a force of 5 N acting on a body of mass 20 kg ?
Q 38.
What are balanced and unbalanced forces?
Q 39.
Fill in the blanks :
When we shake a branch of a mango tree the mangoes fell down, this happens because of ___________.
Q 40.
If the body is found to be accelerated, is the force acting on it balanced or unbalanced?
Q 41.
A bullet of mass 20 gram moving with a velocity of 300 m/s gets embedded in a freely suspended wooden block of mass 880 gram.What is the velocity acquired by the block ?
Q 42.
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 43.
Akhtar,Kiran and Rahul were riding in a motorcar that was moving with a high velocity on an expressway when an insect hit the windshield and got stuck on the windscreen. Akhtar and Kiran started pondering over the situation. Kiran suggested that the insect suffered a greater change momentum as compared to the change in momentum of the motorcar (because the chanee in the velocity of the insect was much more than that of the motorcar). Akhtar said that smce the motorcar was moving with a larger velocity, it exerted a larger force on the insect.And as a result,the insect died.Rahul whUe putting an entirely new explanation said that both the motorcar and the msect experienced the same force and a change in their momentum.Comment on these suggestions.
Q 44.
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 45.
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 46.
Can balanced forces move a body at rest ?
Q 47.
Name the unbalanced force that stops a ball rolling on the ground.
Q 48.
Is momentum a scalar or vector ?
Q 49.
What is the total momentum of the bullet and the gun on firing ?
Q 50.
In the above question,which body undergoes greater change in momentum ?
