Question

You drop a rock off a bridge. When the rock has fallen 4m, you drop a second rock. As the two rocks continue to fall, what happens to their velocities?

(a) Both increase at the same rate.

(b) The velocity of the first rock increases faster than the velocity of the second.

(c) The velocity of the second rock increases faster than the velocity of the first.

(d) Both velocities stay constant.

Short answer

The correct option is (a) Both increase at the same rate.

Step-by-step solution

Step 1. Significance of free fall of a rock

During free-fall, the rock moves in the downward direction under the effect of gravity. In this motion, only the gravitational force acts on the rock. The rock falls with an acceleration equal to the acceleration due to gravity.

Step 2. Determination of velocities of two rocks

The first rock falls 4 m and moves downward with acceleration due to gravity.

Then, the second rock is dropped. The second rock also moves downward with acceleration due to gravity. Both rocks continue to move downward under the same effect.

Velocities of the rocks increase when they are free falling.

Step 3. Determination of the correct option

Options (b) and (c) are incorrect because the velocities of the first and second rocks increase at the same rate. Neither of the rocks moves with a higher velocity.

Option (d) is incorrect because both velocities change at the same rate. They are not constant.

The rate of velocity change for both free-falling rocks is the same. Their velocities increase at the same rate.

Hence, the correct option is (a).