Question:
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 ?
Answer:
Given, mass of hammer(m) = 500g = 0.5 kg
initial velocity of hammer(u) = 50 m/s
final velocity of hammer (v) = 0 m/s
Duration (t) = 0.01s
Using second law of motion, F = ma = m(v - u)/t
⇒ F = 0.5(0 - 50)/0.01 = (0.5 × -50)/0.01 = -2500N ... (answer)
The -ve sign shows the force of 2500N acts in the opposite direction of motion.
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.
On what factor does inertia of a body depend ?
Q 3.
Fill in the blanks :
The study of motion of a body under the action of a force is called ______.
Q 4.
Are action-reaction forces simultaneous ?
Q 5.
Do action-reaction forces produce the same magnitude of acceleration ?
Q 6.
What is the unit of force in c.g.s system?
Q 7.
Can every force produce motion in every object?
Q 8.
In the above question, which body is damaged more ?
Q 9.
Can balanced forces change the shape and size of an object?
Q 10.
What is the total momentum of a bullet and a gun before firing?
Q 11.
Can balanced forces change the shape and size of a body ?
Q 12.
Using second law of motion, derive the relation between force and acceleration.
Q 13.
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 14.
When a branch of a tree is shaken, some of the fruits may fall down.Why ?
Q 15.
Explain why a player lowers his hands while catching a cricket ball.
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.
It is difficult to balance our body when we accidentally slip on a peel of banana. Explain why?
Q 18.
The masses of two objects are 2 kg and 20 kg. Which has greater inertia ?
Q 19.
What acceleration is produced by a force of 5 N acting on a body of mass 20 kg ?
Q 20.
A body of mass 25 kg has momentum of 125 kg m/s. What is the velocity of the body?
Q 21.
What is the SI unit of impulse.
Q 22.
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 23.
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 24.
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 25.
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 26.
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 27.
What a force can do?
Q 28.
A bullet of mass 20 gram moving with a velocity of 300 m/s gets embedded in a freely suspended wooden block of mass 880 gram.What is the velocity acquired by the block ?
Q 29.
Show that kg-
and N-s represent the same quantity.Which is that quantity ?
Q 30.
Explain what is meant by momentum of a body.Is it a scalar or a vector ? What are its units ?
Q 31.
Derive the relation F = ma,where the symbols have their usual meanings.
Q 32.
Establish relation between inertia and mass.
Q 33.
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 34.
Fill in the blanks :
Which has more inertia of Cricket ball or a rubber ball of the same size? __________
Q 35.
What are unbalanced forces ?
Q 36.
In the above question,which body undergoes greater change in momentum ?
Q 37.
Why does a gun recoil on firing ? Obtain an expression for recoil velocity of gun.
Q 38.
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 39.
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 40.
A stone of 1 kg is thrown with a velocity of 20 m s-1 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? (Calculate time taken and acceleration also).
Q 41.
When two objects act on each other, does action-reaction force pair cancel out each other?
Q 42.
If action is always equal to the reaction, explain how a horse can pull a cart.
Q 43.
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 44.
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 45.
Fill in the blanks :
________ is the tendency of an object to resist a change in motion.
Q 46.
Why does a bicycle slow down when the cyclist stop pedalling?
Q 47.
Define 1 Newton force.
Q 48.
What do you mean by a resultant force?
Q 49.
How is force related to acceleration produced in a body by its application?
Q 50.
What is the SI unit of momentum?
