Question

A water tanker filled up to $\frac{2}{3}$rd 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

Answer: (B)

move forward

Basically, the law of motion is that an object at rest stays at rest and an object continues in motion until an external force acts on it.
Inertia is the resistance of any physical object to any change in its state of motion, including changes to its speed and direction. It is the tendency of objects to keep moving in a straight line at constant velocity.

So, on sudden application of brakes on the water tank, the water tank decelerates or may even stop but the water in the tank still has a tendency to move forward due to inertia. Hence the water in the tank would move forward.
A water tanker filled up to two-thirds of its height moving with a uniform speed, on sudden application of the brake, the water in the tank would move forward.