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.
What is the unit of force in c.g.s system?
Q 3.
On what factor does inertia of a body depend ?
Q 4.
Can every force produce motion in every object?
Q 5.
Do action-reaction forces produce the same magnitude of acceleration ?
Q 6.
It is difficult to balance our body when we accidentally slip on a peel of banana. Explain why?
Q 7.
Explain why a player lowers his hands while catching a cricket ball.
Q 8.
What is the SI unit of impulse.
Q 9.
Fill in the blanks :
The study of motion of a body under the action of a force is called ______.
Q 10.
When a branch of a tree is shaken, some of the fruits may fall down.Why ?
Q 11.
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 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 body of mass 25 kg has momentum of 125 kg m/s. What is the velocity of the body?
Q 14.
The masses of two objects are 2 kg and 20 kg. Which has greater inertia ?
Q 15.
Using second law of motion, derive the relation between force and acceleration.
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.
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 18.
Can balanced forces change the shape and size of an object?
Q 19.
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 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.
What is the net momentum of gun and bullet system before firing?
Q 22.
In the above question, which body is damaged more ?
Q 23.
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 24.
Why is the person hurt less when he falls on a spongy surface?
Q 25.
Why does a gunman get a jerk on a firing a bullet ?
Q 26.
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 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.
Name the physical quantity that corresponds to the rate of change of momentum.
Q 29.
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 30.
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 31.
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 32.
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 33.
Name the unbalanced force that stops a ball rolling on the ground.
Q 34.
Name any two applications of the law of conservation of linear momentum.
Q 35.
Which is having higher value of momentum ? A bullet of mass 10 g moving with a velocity of 400 m/s or a cricket ball of mass 400 g thrown with the speed of 90 km/hr.
Q 36.
Fill in the blanks :
________ is the tendency of an object to resist a change in motion.
Q 37.
What is formula of impulse?
Q 38.
Two hockey players of opposite teams,while trying to.hit a hockey ball on the ground collide and immediately become entangled.One has a mass of 60 kg,and was moving with a velocity 5.0 m/s,while the other has a mass of 55 kg and was moving faster with a velocity of 6.0 m/s towards the first player,In which direction and with what velocity will they move after they become entangled ? Assume that the frictional force acting between the feet of the two players and ground is negligible.
Q 39.
What is the total momentum of the bullet and the gun on firing ?
Q 40.
What acceleration is produced by a force of 5 N acting on a body of mass 20 kg ?
Q 41.
What a force can do?
Q 42.
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 43.
When a force acts on a body, what are the two essential effects it can produce?
Q 44.
When you apply a force for a certain amount of time, it creates ________ (fill in the blank).
Q 45.
A motorcar is moving with a velocity of 108 km/h and it takes 4 second to stop after the brakes are applied.Calculate the force exerted by the brakes on the motorcar if its mass alongwith the passengers is 1000 kg.
Q 46.
A force of 5 N gives a mass
an acceleration of 10
,and a mass
,an acceleration of 20
.What acceleration would it give if both the masses were tied together ?
Q 47.
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 48.
What is the other name for Newton's first law of motion ?
Q 49.
Is momentum a scalar or vector ?
Q 50.
State the law of conservation of linear momentum.
