Question:
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?
Answer:
No because these two forces are acting on the same body, these are not due to Newton's third law of motion. These two forces do not form action-reaction pair.
In fact, Newton's first law of motion does apply. Since the TV set is at rest, because these forces are balanced. i.e. FW = - FTable-TV
Force and Laws of Motion
Q 1.
Define momentum of a body.
Q 2.
What is the total momentum of a bullet and a gun before firing?
Q 3.
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 4.
A person in a bus tends to fall backwards, when it starts suddenly ?
Q 5.
Discuss briefly Galileo's ideas about motion.
Q 6.
What is the other name for Newton's first law of motion ?
Q 7.
Are action-reaction forces simultaneous ?
Q 8.
Do action-reaction forces produce the same magnitude of acceleration ?
Q 9.
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 10.
When a force acting on a body has equal and opposite reaction, then why should the body move at all?
Q 11.
On what factor does inertia of a body depend ?
Q 12.
What is one newton force ?
Q 13.
State Newton’s second law of motion and establish that F = ma where symbols have their usual meanings.
Q 14.
Using second law of motion, derive the relation between force and acceleration.
Q 15.
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 16.
Fill in the blanks :
Which has more inertia of Cricket ball or a rubber ball of the same size? __________
Q 17.
A bullet of mass 50 g is fired from a gun of mass 6 kg with a velocity of 400 m/s.Calculate the recoil velocity of the gun.
Q 18.
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 19.
Is force a scalar or a vector ?
Q 20.
Can balanced forces move a body at rest ?
Q 21.
Is momentum a scalar or vector ?
Q 22.
Explain what is meant by momentum of a body.Is it a scalar or a vector ? What are its units ?
Q 23.
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 24.
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 25.
State Law of conservation of momentum.
Q 26.
Law of conservation of momentum is applicable to an isolated system. What do you mean by an isolated system?
Q 27.
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 28.
A 8000 kg engine pulls a train of 5 wagons, each of 2000 kg, along a horizontal track. If the engine exerts a force of 40000 N and the track offers a friction force of 5000 N, then calculate:
(a) the net accelerating force;
(b) the acceleration of the train; and
(c) the force of wagon 1 on wagon 2.
Q 29.
Fill in the blanks :
The study of motion of a body under the action of a force is called ______.
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.
Can balanced forces change the shape and size of an object?
Q 32.
Which Newton's law is also known as the Law of Inertia?
Q 33.
Name the physical quantity that corresponds to the rate of change of momentum.
Q 34.
Which would require a greater force : accelerating a 2 kg mass at 5
or a 4 kg mass at 2
?
Q 35.
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 36.
A 150 g ball travelling at 30 m/s strikes the palm of a player’s hand and is stopped in 0 06 sec. Calculate the force exerted by the ball on the hand.
Q 37.
A bullet of mass 10 g travelling horizontally with a velocity of 150
strikes a block and comes to rest in 0.03 s. Calculate the distance of penetration of the bullet into the block.Also, calculate the magnitude of the force exerted by the wooden block on the bullet.
Q 38.
What is the SI unit of force ?
Q 39.
The masses of two objects are 2 kg and 20 kg. Which has greater inertia ?
Q 40.
What is the SI unit of momentum ?
Q 41.
What is the total momentum of the bullet and the gun on firing ?
Q 43.
Explain why a player lowers his hands while catching a cricket ball.
Q 44.
Why does a gun recoil on firing ? Obtain an expression for recoil velocity of gun.
Q 45.
Which of the following has more inertia:
(a) a rubber ball and a stone of the same size?
(b) A bicycle and a train?
(c) A five-rupee coin and a one-rupee coin?
Q 46.
A body of mass 25 kg has momentum of 125 kg m/s. What is the velocity of the body?
Q 47.
Why is it advised to tie any luggage kept on the roof of a bus with a rope?
Q 48.
What's the relation between 1N and 1 dyne?
Q 49.
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 50.
How Newton's Second law of motion is different from First law?
