Question

A water tanker filled up to 2/3 of its height is moving with a uniform speed. On sudden application of the brake, the water in the tank would:
A. Move backward.
B. Move forward.
C. Be unaffected.
D. Rise upwards.

Answer 1

Hint: Newton’s first law of motion states that a body continues to be in a state of rest or motion and it will remain moving in the same direction with the same velocity unless we apply some external force on it.

Complete step by step answer:
Inertia is the property of an object by virtue of which it neither changes its present state nor it tends to change the present state. It is the inherent property of each object. In other words, the property by virtue of which it has a tendency to resist the change in its state of rest or state of motion.
A body in a state of motion possesses inertia of motion and it continues to be in the state of motion with the same speed in the same direction in a straight line and it remains in that state until we apply some external force to it.
A water tanker which is filled up to two-third of its height is moving with a uniform i.e., constant speed. When the brakes are applied suddenly, the tanker comes to a rest after a few seconds but the water continues to move in the same direction i.e., forward direction due to inertia of motion. The lower portion of water is in contact with the surface of the tanker, so when brakes are applied the lower portion of water comes to rest but the upper portion continues to be in motion. Thus, the water in the tank would move forward.
Therefore, option B is correct.

Note: Initially the water in the tank is in a state of motion along with the tanker. As the brakes are applied, the lower portion of water being in contact with the tanker comes to rest and the upper part remains in the state of motion.