 # Important questions on Force ,Momentum and Laws of Motion

Question 1.
(a) Define momentum. Write its SI unit.
(b) A bullet of mass 0.02 kg is fired from a gun weighing 7.5 kg if the initial velocity of bullet is 200 m/s. Calculate the speed with which the gun recoils.

Question 2.
Why is it advised to tie the luggage with a rope on the roof buses?

Question 3.
State any three changes that a force brings about on a body. Give one example of each.

Question 4.
Tabulate two differences between balanced and unbalanced forces. Write one example of each.
Question 5.
A book slides down a table top and comes to rest position after a certain distance. Name the force acting on the book. What types of forces are acting on the book? (Balanced/ unbalanced). Which force brought the book to rest?

Question 6..
The mud particles sticking on the rim of a bicycle wheel leave the rim of the wheel tangentially when it starts moving. Explain.

Question 7.
When a motor car makes a sharp turn at a high speed, we tend to get thrown to one side. Why?

Question 8..
What do you understand by inertia? Do all bodies have the same inertia? Illustrate giving an example.
Question 9..
State reason for the following:
a.A person is hit harder, when the person falls on a hard floor than when he falls on sand or cotton.
b.A gunman gets jerk in backward direction while firing a gun.
c.A bullet fired on a glass window makes a fine hole while a stone smashes when hits it.

Question 10.
A passenger in a moving train tosses a coin which falls behind him. It means that motion of the train is
(a) accelerated
(b) uniform
(c) retarded
(d) along circular tracks

Question 11.
A stone of mass 1 kg is thrown with a velocity 20 m/s 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 ice?

Question 12.
State Newton’s second law of motion and prove that Newton’s first law of motion is a special case of Newton’s second law of motion.
Question 13.
(i) What is meant by momentum of a body? How can it be measured? Write its SI units.
(ii) Explain how does Newton’s first law give the qualitative definition of force?
Question 14.
Two objects A and B, having mass 100 kg and 75 kg, moving with velocity 40 km/hr and 6 km/hr respectively. Answer the following:
a.Which will have greater inertia?
b.Which will have greater momentum?
c.Which will stop first if equal negative acceleration is applied on both?
d.Which will travel greater distance?
e.Which will impart greater impulse if collides with a wall?

Question 15.
(i) Define momentum. Write its SI unit.
ii) How much momentum will an object of mass 10 kg transfer to the floor if it falls from a height of 5 m? (g = 10 m/s2)
(iii) Explain how a karate player can break a pile of tiles with a single blow of his hand.

Question 16.
A truck of mass M is moved under a force F. If the truck is then loaded with an object equal to the mass of the truck and the driving force is halved,then how does the acceleration change?.

Question 17.
Do action and reaction act on the same body or on different bodies? Explain your answer with the help of example. How are they related in magnitude and direction? Write the total momentum of the gun and the bullet before firing.
Question 18.
State reason for the following:
a.A runner presses the ground with his feet before he starts his run.
b.To take the boat away from the bank of a river, the boat man pushes the bank with an oar.

Question 19.
Give an example to show that friction is an important factor in satisfying Newton’s third law of motion.
Question 20.
(a) State the law of conservation of momentum.
(b) A boy of mass 60 kg running at 3 m/s jumps on to a trolley of mass 140 kg moving with a velocity of 1.5 m/s in the same direction.
Find their common velocity.

Question 22.
A bullet of mass 10 g moving with a velocity of 400 m/s gets embedded in a freely suspended wooden block of mass 900 g. what is the velocity acquired by the block?

Question 24.
A man weighing 60 kg runs along the rails with a velocity of 18 km/h and jumps into a car of mass 1 quintal (100 kg) standing on the rails. Calculate the velocity with which car will start travelling along the rails.

Question 25.
State the law of conservation of momentum.
Using this law explain why a gun recoils.
Question 26.
A stone released from the top of a tower of height 19.6 m, calculate its final velocity just before touching the ground. (Take g = 9.8 m/s2)

Question 27.
A boy of mass 50 kg running 5 m/s jumps on to a 20 kg trolley travelling in the same direction at 1.5 m/s. find their common velocity.

Question 28.
Car A of mass 1500 kg travelling at 25 m/s collides with another car B of mass 1000 kg travelling at 15 m/s in the same direction. After collision, the velocity of car A becomes 20 m/s. Calculate the velocity of car B after collision.

## Law of Conservation of Momentum Long answer type questions

Question 1.
(a) State law of conservation of momentum. Write SI unit of momentum.
(b) Two cars each of mass 1000 kg are moving in a straight line but in opposite directions. The velocity of each car is 5 m/s before the collision during which they stick together. What will be the velocity of the combined cars after collision?

Question 2.
(a) Define momentum. Write its SI unit.
(b) A car and a truck have same momentum. Whose velocity is more and why?
(c) A bullet of mass 20 g moving with a speed of 500 m/s strikes a wooden block of mass 1 kg and gets embedded in it. Find the speed with which block moves along with the bullet.

Question 3.
Prove the law of conservation of momentum with clear explanation, diagram and equation.
Question 4.
(a) State law of conservation of momentum. Express it mathematically, when two bodies of masses $m_1$ and $m_2$ moving in same direction along same straight line with velocities $u_1$ and $u_2$ respectively, collide and their respective velocities after collision become $v_1$ and $v_2$.
(b) A hammer of mass 500 g moving with 50 m/s strikes a nail. The nail stops the hammer in a small time interval of 0.01/s. what is the change in momentum suffered by the hammer? Also calculate the force of the hammer on the nail. What will be the force of the nail on the hammer? Give reason for your answer.

Question 5.
Name and define the various types of inertia. Illustrate each of them with suitable example.

Question 6.
(i) Define momentum. State its SI unit.
(ii) An object of mass 50 kg is accelerated uniformly from a velocity of 4 m/s to 8 m/s in 8 s. calculate the initial and final momentum of the object. Also find the magnitude of the force exerted on the object.

## INTERESTING NUMERICALS

Question 1.
A bullet of 10 g strikes a sand bag at a speed of 103 m/s and gets embedded after travelling 5 cm. Calculate
(i) the resistive force exerted by the sand on the bullet.
(ii) the time taken by the bullet to come to rest.

Question 2.
A force of 5 N produces an acceleration of 8 m/s2 on a mass $m_1$ and an acceleration of 24 m/s2 on a mass $m_2$. What acceleration would the same force provide if both the masses are tied together?

Question 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?

Reference Books for class 9 science

Given below are the links of some of the reference books for class 9 science.

These books by S.Chand Publications are detailed in their content and are must have books for class 9 students. Some other books that might be worth considering are
1. Oswaal CBSE Question Bank Class 9 Science Chapterwise & Topicwise We all know importance of practicing what we have studied. This book is perfect for practicing what you have learned and studied in the subject.
2. Pearson Foundation Series (IIT-JEE/NEET) Physics, Chemistry, Maths & Biology for Class 9 (Main Books) | PCMB Combo These Foundation books would be helpful for students who want to prepare for JEE/NEET exams. Only buy them if you are up for some challenge and have time to study extra topics. These might be tough for you and you might need extra help in studying these books.
3. Foundation Science Physics for Class - 9 by H.C. Verma This is one of my favorite Physics book for class 9. Most of the book is within the limits of CBSE syllabus. It might overwhelm you with its language but I feel if you can understand the content is authentic with plenty of problems to solve.

You can use above books for extra knowledge and practicing different questions.

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