Newton’s Laws of Motion Physics - Newton’s Laws of Motion

The force exerted by the floor of an elevator on the foot of a person standing there is more than the weight of the person if the elevator is:

1. Going up and slowing down.
2. Going up and speeding up.
3. Going down and slowing down.
4. Going down and speeding up.

A block of mass 10kg is suspended through two light spring balances as shown in figure:

1. Both the scales will read 10kg.
2. Both the scales will read 5kg.
3. The upper scale will read 10kg and the lower zero.
4. The readings may be anything but their sum will he 10kg.

A force F₁ acts on a particle so as to accelerate it from rest to a velocity v. The force F₁ is then replaced by F₂ which decelerates it to rest:

1. F₁ must be equal to F₂.
2. F₁ may be equal to F₂.
3. F₁ must be unequal to F₂.
4. None of these.

A free ²³⁸U nucleus kept in a train emits an alpha particle. When the train is stationary, a nucleus decays and a passenger measures that the separation between the alpha particle and the recoiling nucleus becomes x at time t after the decay. If the decay takes place while the train is moving at a uniform velocity v, the distance between the alpha particle and the recoiling nucleus at a time t after the decay as measured by the passenger is:

1. x + vt
2. x - vt
3. x
4. Depends on the direction of the train.

Two blocks A and B of mass m_A and m_B respectively are kept in contact on a frictionless table. The experimenter pushes the block A from behind so that the blocks accelerate. If the block A exerts a force F on the block B, what is the force exerted by the experimenter on A?

Raindrops of radius 1mm and mass 4mg are falling with a speed of 30m/s on the head of a bald person. The drops splash on the head and come to rest. Assuming equivalently that the drops cover a distance equal to their radii on the head, estimate the force exerted by each drop on the head.

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

An object is placed far away from all the objects that can exert force on it. A frame of reference is constructed by taking the origin and axes fixed in this object. Will the frame be necessarily inertial?

The acceleration of a particle is zero as measured from an inertial frame of reference. Can we conclude that no force acts on the particle?

A car moving at 40km/h is to be stopped by applying brakes in the next 4.0m. If the car weighs 2000kg, what average force must be applied on it?

A person drops a coin. Describe the path of the coin as seen by the person if he is in:

1. A car moving at constant velocity.
2. In a freely falling elevator.

If you jump barefooted on a hard surface, your legs get injured. But they are not injured if you jump on a soft surface like sand or pillow. Explain.

A block of mass 2kg placed on a long frictionless horizontal table is pulled horizontally by a constant force F. It is found to move 10m in the first two seconds. Find the magnitude of F.

Both the springs shown in figure are unstretched. If the block is displaced by a distance x and released, what will be the initial acceleration?

Calculate the tension in the string shown in figure. The pulley and the string are light and all surfaces are frictionless. Take g = 10m/s².

Two blocks of equal mass m are tied to each other through a light string. One of the blocks is pulled along the line joining them with a constant force F. Find the tension in the string joining the blocks.

A monkey of mass 15kg is climbing on a rope with one end fixed to the ceiling. If it wishes to go up with an acceleration of 1m/s², how much force should it apply to the rope? If the rope is 5m long and the monkey starts from rest, how much time will it take to reach the ceiling?

It is sometimes heard that inertial frame of reference is only an ideal concept and no such inertial frame actually exists. Comment.

A man has fallen into a ditch of width d and two of his friends are slowly pulling him out using a light rope and two fixed pulleys as shown in figure. Show that the force (assumed equal for both the friends) exerted by each friend on the road increases as the man moves up. Find the force when the man is at a depth h.

Suppose you are running fast in a field when you suddendly find a snake in front of you. You stop quickly. Which force is responsible for your deceleration?

A person is standing on a weighing machine placed on the floor of an elevator. The elevator starts going up with some acceleration, moves with uniform velocity for a while and finally decelerates to stop. The maximum and the minimum weights recorded are 72kg and 60kg. Assuming that the magnitudes of the acceleration and the deceleration are the same, find:

1. The true weight of the person.
2. The magnitude of the acceleration. Take g = 9.9m/s².

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In a TV picture tube electrons are ejected from the cathode with negligible speed and reach a velocity of 5 × 10⁶m/s in travelling one centimeter. Assuming straight line motion, find the constant force exerted on the electron. The mass of the electron is 9.1 × 10^-31kg.

In the previous problem, suppose m₂ = 2.0kg and m₃ = 3.0kg. What should be the mass m so that it remains at rest?

A pendulum bob of mass 50g is suspended from the ceiling of an elevator. Find the tension in the string if the elevator:

1. Goes up with acceleration 1.2m/s².
2. Goes up with deceleration 1.2m/s².
3. Goes up with uniform velocity.
4. Goes down with acceleration 1.2m/s².
5. Goes down with deceleration 1.2m/s².
6. Goes down with uniform velocity.

Find the acceleration of the block of mass M in the situation shown in figure. All the surfaces are frictionless and the pulleys and the string are light.

Figure shows a man of mass 60kg standing on a light weighing machine kept in a box of mass 30kg. The box is hanging from a pulley fixed to the ceiling through a light rope, the other end of which is held by the man himself. If the man manages to keep the box at rest, what is the weight shown by the machine? What force should he exert on the rope to get his correct weight on the machine?