Question:
Define force of friction.
Answer:
The force acting between any two surfaces in contact and tending to oppose motion is called force of friction.
Force and Laws of Motion
Q 1.
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 2.
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 3.
What is the total momentum of a bullet and a gun before firing?
Q 4.
Can balanced forces change the shape and size of an object?
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.
Are action-reaction forces simultaneous ?
Q 8.
Using second law of motion, derive the relation between force and acceleration.
Q 9.
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 10.
Can every force produce motion in every object?
Q 11.
Can balanced forces change the shape and size of a body ?
Q 12.
When a branch of a tree is shaken, some of the fruits may fall down.Why ?
Q 13.
Do action-reaction forces produce the same magnitude of acceleration ?
Q 14.
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 15.
State Law of conservation of momentum.
Q 16.
In the above question, which body is damaged more ?
Q 17.
What is the unit of force in c.g.s system?
Q 18.
It is difficult to balance our body when we accidentally slip on a peel of banana. Explain why?
Q 19.
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 20.
Fill in the blanks :
The momentum of an object is the product of its _____ and _______ and has the same direction as that of the ________.
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 ? What would be the acceleration if the mass were halved ?
Q 23.
Why does a person in a bus tend to fall forward when it stops suddenly ?
Q 24.
A body of mass 25 kg has momentum of 125 kg m/s. What is the velocity of the body?
Q 25.
A motorcar of mass 1200 kg is moving along a straight line with a uniform velocity of 90 km/h. Its velocity is slowed down to 18 km/h in 4 s by an unbalanced external force. Calculate the acceleration and change in momentum. Also calculate the magnitude of the force required.
Q 26.
Fill in the blanks :
When a car enters a curved path, the person sitting in it is thrown outwards. This is because of the property of ______________.
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.
Give an example that force can make a stationary body move.
Q 29.
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 30.
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 31.
Why does a gun recoil on firing ? Obtain an expression for recoil velocity of gun.
Q 32.
Give atleast four applications of Newton’s second law of motion.
Q 33.
Why is it advised to tie any luggage kept on the roof of a bus with a rope?
Q 34.
Fill in the blanks :
An imaginary co-ordinate system which is either at rest or in uniform and where Newton's laws are valid is called an _______ frame of reference.
Q 35.
When a force acts on a body, what are the two essential effects it can produce?
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.
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 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 are balanced forces ?
Q 40.
What are unbalanced forces ?
Q 41.
Discuss briefly Galileo's ideas about motion.
Q 42.
What a force can do?
Q 43.
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 44.
Law of conservation of momentum is applicable to an isolated system. What do you mean by an isolated system?
Q 45.
The following is the distance-time table of an object in motion:
| Time in seconds |
Distance in meters |
| 0 |
0 |
| 1 |
1 |
| 2 |
8 |
| 3 |
27 |
| 4 |
64 |
| 5 |
125 |
| 6 |
216 |
| 7 |
343 |
(a) What conclusion can you draw about the acceleration? Is it constant, increasing, decreasing, or zero?
(b) What do you infer about the forces acting on the object?
Q 46.
Force can change the shape and size of an object. Give an example.
Q 47.
Why does a bicycle slow down when the cyclist stop pedalling?
Q 48.
What are balanced forces?
Q 49.
What is the SI unit of momentum?
Q 50.
Which principle is involved in the working of a jet plane?
