Question:
What are contact forces? Give examples
Answer:
Contact forces are forces in which the two interacting objects are physically in contact with each other. Examples of contact forces are:
- Tension force
- Normal force
- Air resistance
- Buoyant force
- Friction force
Force and Laws of Motion
Q 1.
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 2.
What is the total momentum of a bullet and a gun before firing?
Q 3.
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 4.
Can balanced forces change the shape and size of an object?
Q 5.
Can balanced forces change the shape and size of a body ?
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.
Fill in the blanks :
The study of motion of a body under the action of a force is called ______.
Q 9.
Are action-reaction forces simultaneous ?
Q 10.
What is the unit of force in c.g.s system?
Q 11.
Using second law of motion, derive the relation between force and acceleration.
Q 12.
Can every force produce motion in every object?
Q 13.
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 14.
In the above question, which body is damaged more ?
Q 15.
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 16.
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 17.
When a branch of a tree is shaken, some of the fruits may fall down.Why ?
Q 18.
It is difficult to balance our body when we accidentally slip on a peel of banana. Explain why?
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.
What acceleration is produced by a force of 5 N acting on a body of mass 20 kg ?
Q 21.
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 22.
State Law of conservation of momentum.
Q 23.
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 24.
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 25.
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 26.
Show that kg-
and N-s represent the same quantity.Which is that quantity ?
Q 27.
Explain why a player lowers his hands while catching a cricket ball.
Q 28.
Define 1N (Newton).
Q 29.
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 30.
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 31.
Fill in the blanks :
When a hanging carpet is beaten with stick, the dust particles start coming out of it. It is due to ______________.
Q 32.
What are balanced forces?
Q 33.
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 34.
A stone of 1 kg is thrown with a velocity if 20
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 ?
Q 35.
Can balanced forces move a body at rest ?
Q 36.
The masses of two objects are 2 kg and 20 kg. Which has greater inertia ?
Q 38.
Explain what is meant by momentum of a body.Is it a scalar or a vector ? What are its units ?
Q 39.
Discuss briefly Galileo's ideas about motion.
Q 40.
Why does a gun recoil on firing ? Obtain an expression for recoil velocity of gun.
Q 41.
Give atleast four applications of Newton’s second law of motion.
Q 42.
What a force can do?
Q 43.
Two persons manage to push a motorcar of mass 1200 kg at a uniform velocity along a level road. The same motorcar can be pushed by three persons to produce an acceleration of 0.2m s-2. With what force does each person push the motorcar?
(Assume that all persons push the motorcar with the same muscular effort.)
Q 44.
Fill in the blanks :
Newton's second law of motion states that the rate of change of ______ of a body is directly proportional to the force and takes place in the same direction as the ______.
Q 45.
Fill in the blanks :
Which has more inertia of Cricket ball or a rubber ball of the same size? __________
Q 46.
Fill in the blanks :
A cyclist on a levelled road does not come to rest immediately even he stops pedalling. It is due to ______________.
Q 47.
Fill in the blanks :
________ is a measure of intertia.
Q 48.
Why does a bicycle slow down when the cyclist stop pedalling?
Q 49.
What are unbalanced forces?
Q 50.
When a force acts on a body, what are the two essential effects it can produce?
