Question:
Derive the unit of force using the second law of motion. A force of 5 N produces an acceleration of on a mass and an acceleration of 24 on a mass .What acceleration would the same force provide if both the masses are tied together ?
Answer:
For unit of force, refer to Art. 2.12, Page 85.
From F = ma, = =kg and ==kg
Total m=+=+==kg.
Net acceleration, a = ==6 m/s.
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.
Can balanced forces change the shape and size of an object?
Q 4.
What is the total momentum of a bullet and a gun before firing?
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.
Using second law of motion, derive the relation between force and acceleration.
Q 8.
Can balanced forces change the shape and size of a body ?
Q 9.
When a branch of a tree is shaken, some of the fruits may fall down.Why ?
Q 10.
Are action-reaction forces simultaneous ?
Q 11.
Do action-reaction forces produce the same magnitude of acceleration ?
Q 12.
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 13.
Can every force produce motion in every object?
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.
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 20.
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 21.
Why does a person in a bus tend to fall forward when it stops suddenly ?
Q 22.
A body of mass 25 kg has momentum of 125 kg m/s. What is the velocity of the body?
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.
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 25.
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 26.
Give an example that force can make a stationary body move.
Q 27.
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 28.
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 30.
Why does a gun recoil on firing ? Obtain an expression for recoil velocity of gun.
Q 31.
Give atleast four applications of Newton’s second law of motion.
Q 32.
Why is it advised to tie any luggage kept on the roof of a bus with a rope?
Q 33.
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 34.
When a force acts on a body, what are the two essential effects it can produce?
Q 35.
What is the momentum of a man of mass 75 kg when he walks with a velocity of 2 m/s ?
Q 36.
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 37.
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 38.
What are balanced forces ?
Q 39.
What are unbalanced forces ?
Q 40.
The masses of two objects are 2 kg and 20 kg. Which has greater inertia ?
Q 41.
Discuss briefly Galileo's ideas about motion.
Q 42.
Explain why a player lowers his hands while catching a cricket ball.
Q 43.
State and explain Newton’s third law of motion.How will you prove it experimentally ?
Q 44.
What a force can do?
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.
Law of conservation of momentum is applicable to an isolated system. What do you mean by an isolated system?
Q 47.
A bullet of mass 10 g travelling horizontally with a velocity of 150 m/s strikes a stationary wooden 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 48.
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 49.
The speed-time graph of a car is shown below. The car weighs 1000kg.
(i) Find the distance covered by the in fits two seconds.
(ii) Find how much force is applied by the car brakes in the fifth second so that the car comes to an halt by sixth second.
Q 50.
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.
