When an air bubble moves up from the bottom of a lake

Options

A. its velocity decreases and becomes zero
B. its velocity increases and becomes constant
C. its ac celeration decreases and becomes zero
D. its ac celeration increases and becomes constant

Answer

B, C

Explanation

When an air bubble is inside the water, the upward thrust on bubble due to water is more than the weight of air bubble. As a result of it, the bubble is ac celerated upwards aned its velocity increases. Then the viscous force comes into play. Which also increases and finally the bubble moves with a constant terminal velocity. As the bubble rises up, the pressure on bubble decreases, i.e., the upward thrust on the bubble decreases, therefore, the ac celeration of bubble decreases, when the bubble movies with terminal velocity, then ac celeration becomes zero.