Question:
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.
Answer:
Initially both rifle and bullet are at rest. Given,
mass of rifle (m1) = 4 kg
initial velocity of rifle (u1) = 0 m/s
final velocity of rifle (v1) = ?
mass of bullet (m2) = 50g = 50 × 10-3 kg = 0.05 kg
initial velocity of bullet (u2) = 0 m/s
final velocity of bullet (v2) = 35 m/s
Applying law of conservation of momentum,
total initial momentum = total final momentum
i.e. (m1u1) + (m2u2) = (m1v1) + (m2v2)
⇒ 0 + 0 = (4v1) + (0.05 × 35)
⇒ - 4v1 = 0.05 × 35
⇒ v1 = - 0.4375 m/s ... (answer)
The negative sign indicates that rifle recoils in opposite direction to bullet i.e. backwards
Force and Laws of Motion
Q 1.
Are action-reaction forces simultaneous ?
Q 2.
What is the unit of force in c.g.s system?
Q 3.
Explain why a player lowers his hands while catching a cricket ball.
Q 4.
Can every force produce motion in every object?
Q 5.
On what factor does inertia of a body depend ?
Q 6.
Do action-reaction forces produce the same magnitude of acceleration ?
Q 7.
Fill in the blanks :
The study of motion of a body under the action of a force is called ______.
Q 8.
Can balanced forces change the shape and size of an object?
Q 9.
What is the SI unit of impulse.
Q 10.
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 11.
It is difficult to balance our body when we accidentally slip on a peel of banana. Explain why?
Q 12.
When a branch of a tree is shaken, some of the fruits may fall down.Why ?
Q 13.
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 14.
A man pushes a box of mass 50 kg with a force of 80 N. What will be the acceleration of the box due to this force? What would be the acceleration if the mass were doubled ?
Q 15.
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 16.
A body of mass 25 kg has momentum of 125 kg m/s. What is the velocity of the body?
Q 17.
Using second law of motion, derive the relation between force and acceleration.
Q 18.
The masses of two objects are 2 kg and 20 kg. Which has greater inertia ?
Q 19.
In the above question, which body is damaged more ?
Q 20.
What is the net momentum of gun and bullet system before firing?
Q 21.
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 22.
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 23.
The following is the distance-time table of an object in motion :
| Time(s) | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
|---|
|
| Distance (m) | 0 | 1 | 8 | 27 | 64 | 125 | 216 | 343 |
|---|
(a) What conclusion can you draw about the acceleration ? Is it constant ? increasing ? decreasing ?zero ?
(b) What do you infer about the forces acting on the object ?
Q 24.
What acceleration is produced by a force of 5 N acting on a body of mass 20 kg ?
Q 25.
Why does a gunman get a jerk on a firing a bullet ?
Q 26.
Name the unbalanced force that stops a ball rolling on the ground.
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.
What is formula of impulse?
Q 29.
State Newton’s first law of motion. Hence define force and inertia.
Q 30.
Name the physical quantity that corresponds to the rate of change of momentum.
Q 31.
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 32.
Can balanced forces stop a moving body ?
Q 33.
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 34.
What is the momentum of an object of mass m,moving with a velocity v ?(a)
(b)
(c)
(d) mv
Q 35.
State the law of conservation of linear momentum.
Q 37.
State why Newton's first law of motion is called law of inertia.
Q 38.
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 39.
Identify the action and reaction forces in the following cases:
(a) A television (TV) lying on a table
(b) Pushing a wall with your hand
(c) Firing a bullet from a gun.
(d) Walking of a person on a ground.
Q 40.
Two objects, each of mass 1.5 kg, are moving in the same straight line but in opposite directions. The velocity of each object is 2.5 m/s before the collision during which they stick together. What will be the velocity of the combined object after collision?
Q 41.
What is the total momentum of a bullet and a gun before firing?
Q 42.
Why is the person hurt less when he falls on a spongy surface?
Q 43.
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 44.
In the above question,which body undergoes greater change in momentum ?
Q 45.
Name the three types of inertia.
Q 46.
Define momentum of a body.
Q 47.
Explain what is meant by momentum of a body.Is it a scalar or a vector ? What are its units ?
Q 48.
Discuss briefly Galileo's ideas about motion.
Q 49.
Give atleast four applications of Newton’s second law of motion.
Q 50.
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 ______________.
