Third Law of Motion

Q.

A shell of mass 0.020 kg is fired by a gun of mass 100 kg. If the muzzle speed of the shell is $80m{s}^{-1}$, what is the recoil speed of the gun?

Q.

A horse is harnessed to a cart. If the horse tries to pull the cart, the horse must exert a force on the cart. By Newton's third law the cart must then exert an equal and opposite force on the horse. Since the two forces are equal and opposite, they must add to zero, so Newton's second law tells us that the acceleration of the system must be zero and therefore no matter how hard the horse pulls, it can never move the cart.

1. True the horse won't be able to move the cart.

2. False, the horse will move the cart as this is a non inertial frame and newton's laws are not valid here

3. False, the horse will move the cart as air friction is the external force on the system.

4. False, the horse cart system will move as friction from ground is the external force on the system.

Q.

Where do we apply a force while walking?

Q.

If you are pushing the wall then the wall will also push you back according to 3rd law.. so which is action and which is reaction.

1. The force with which you push the wall is the action and the force with which the wall pushes you is the reaction.

2. Any one of the force can be the action and the other is reaction.

3. None of the forces here are action and reaction.

4. The force with which the wall pushes you is the action and the force with which you push the wall is the reaction

Q. A gun fires 10 bullets/sec each of mass 10 gm, with a muzzle velocity of $50\frac{m}{s}$. Find the force required to hold the gun in position.

Q. If a car's engine apply force equal to the kinetic friction then wouldn't the net force=0 =>
the car is at rest? Is it possible for the car to have uniform velocity on the road despite friction?

Q.

According to Newton's third law each team pulls the opposite team with equal force in a game of tug of war. Why then does one team win and the other lose?

1. If team 1 is winning, it is because team 1 is applying a greater force on the rope

2. The losing team applies a greater force on the ground

3. The losing team is applying a greater force on the rope

4. None of these

Q. A man tries to remain in steady state by pushing his feet and hands against two parallel walls. Then for equilibrium

1. Force of friction should be equal on the two walls.
2. Force exerted by him on both walls should be equal and the walls should not be frictionless
3. He should press his feet with greater force.
4. Coefficient of friction should be equal for both walls.

Q.

What are Newtons laws?

Q. A book is lying on a table.The weight of book & the normal force by table on the book are equal in magnitude and opposite in direction. Is this an example of Newton's third law?

1. Definitely yes
2. May be
3. Never

Q.

Explain how friction helps us to walk.

Q. A uniform square plate has a small piece $Q$ of an irregular shape removed and glued to the centre of the plate leaving a hole behind $\left(\text{figure}\right).$ the $COM$ of the plate is now in the following quadrant of $x-y$ 𝑝𝑙𝑎𝑛𝑒,

1. $III$
2. $II$
3. $IV$
4. $I$

Q. A girl of mass $40\text{kg}$ jumps with horizontal velocity $5\text{m/s}$ onto a stationary cart of mass $3\text{kg}$ with frictionless wheels. Find her velocity as the cart starts moving.

1. $4.65\text{m/s}$
2. $5.65\text{m/s}$
3. $6.65\text{m/s}$
4. $0\text{m/s}$

Q. What is equilibrium of a body on a rough inclined plane? Topic:friction

Q.

A trolley of mass 300 kg carrying a sandbag of 25 kg is moving uniformly with a speed of 27 km/h on a frictionless track. After a while, sand starts leaking out of a hole on the floor of the trolley at the rate of 0.05 kg s^–1. What is the speed of the trolley after the entire sand bag is empty?

Q. Action is the cause of reaction .Then , if we push the wall and wall pushes us , we are being pushed only when we push the wall . Hence here our force creates a opposite play . Then Why can't we say the force we created here's action instead of saying any of the 2 forces would be action and the other is reaction ?

Q.

Assertion (A): When a person swims, he pushes the water in the same direction as his motion.
Reason (R): Both action and reaction act on the same body.

1. A and R are true and R is the correct explanation of A.

2. A and R are true, but R is not the correct explanation of A.

3. A is true but R is false.

4. Both A and R are false.

Q. Along a streamline

1. the velocity of a fluid particle remains constant.

2. the velocity of all fluid particles at a given instant is constant.

3. the speed of a fluid particle remains constant.
4. the velocity of all fluid particles crossing a given position is constant.

Q. A ball of mass 𝑚 moving with velocity $\overrightarrow{u}={\overrightarrow{u}}_x\hat{i}+{\overrightarrow{u}}_y\hat{j}$ hits a vertical wall of infinite mass as shown in the figure. The ball slips up along the wall for the duration of collision and there is friction between the ball and the wall. Neglect the effect of gravity. Pick up the correct alternative

1. The impulse provided by frictional force to the ball for the duration of collision cannot be neglected in comparison to impulse provided by normal reaction.
2. The wall provides the ball with net impulse along the negative 𝑥-axis for the duration of collision.
3. The collision changes only the 𝑥-component of velocity of the ball.
4. The collision changes only the 𝑦−component of velocity of the ball.

Q. Two masses M and m are connected to the ends of a string passing over a smooth pulley. The tension in the string is T and the masses are moving with an acceleration a. If the masses are interchanged then what will be its effect on a and T? Will they change

Q. THE FORMULA OF FORCE IS F=ma, BUT WHAT WILL BE THE FORCE APPLIED IF AN OBJECT IS MOVING, BUT ACCELERATION IS NOT THERE i.e THE OBJECT MOVES WITH UNIFORM SPEED OR VELOCITY.

Q.

In a tug of war, two teams are pulling the rope such that the ribbon of the rope is not moving. What is the magnitude of the resultant force on the rope? Explain.

Q.

Give two examples illustrating Newtons third law of motion.

Q. (ii) Ten one-rupee coins are put on top of each other on a table. Each coin has a mass $m$. Given the magnitude and direction of
the force on the $7^{th}$ coin by the eight coin.

(iii)Ten one-rupee coins are put on top of each other on a table. Each coin has a mass $m$. Given the magnitude and direction of
"the reaction of the $6^{th}$ coin on the $7^{th}$ coin"

Q.

what is action reaction force?

Q. There are three Newton's laws of motion namely first, second and third laws.We can derive

1. Second and third laws from the first law.
2. First and second laws from the third law.
3. Third and first laws from the second law.
4. All the three laws are independent of each other.

Q.

Three spring scales (need not be identical) are connected along a straight line as shown in the figure:

The scale on the left is attached to the wall and the scale on the right is pulled with a force of 15N. The reading of the leftmost and middle scale are respectively:

1. 15N each

2. 5N and 10N

3. 10N and 15N

4. 10N and 5N

Q. A shell of mass 200 g is fired by a gun of mass 100 kg. If the muzzle speed of the shell is 80 $m{s}^{-1}$, then the recoil speed of the gun is:

1. 8 $cm{s}^{-1}$
2. 8$m{s}^{-1}$
3. 2$m{s}^{-1}$
4. 16 $cm{s}^{-1}$

Q.

A gun recoils backward the same as the bullet moving forward. Is it so?

Q. A jet engine works on the principle of

1. Conservation of energy
2. Conservation of momentum
3. Conservation of temperature
4. Conservation of mass