A bus is moving forward at 20 m/s. A student on the bus throws a tenis ball horizontally at 15 m/s toward the front of the bus. From the perspective of an observer on the sidewalk
outside the bus, the tennis ball appears to move at -
A 5 m/s
B 15 m/s
C 20 m/s
D 35 m/s

D: 35 m/s

Explanation:

The bus is moving at a speed of 20 m/s.

Thus; v_bus = 20 m/s

Tennis ball thrown horizontally towards the front of the bus is given as 15 m/s.. Thus, v_ball = 15 m/s

No, due to the fact that the bus and the ball are moving at the same time, an observer will think the speed is the sum of that of the ball and the bus.

Thus, it will appear to an observer on the sidewalk that the speed is; v_bus + v_ball = 20 + 15 = 35 m/s