Bob is coming toward you at a speed of 75 km/hr.You throw a baseball in his direction at 75 km/hr.What does he see the ball doing?

Question

Quizplus · Accepted Answer

According to the principle of addition of velocities, the relative velocity of the ball as observed by Bob will be the sum of the velocities of the ball and Bob. As Bob is coming towards the ball at 75 km/hr, the relative velocity of the ball as observed by Bob will be:

Relative velocity = velocity of ball + (-velocity of Bob)
Relative velocity = 75 km/hr + (-75 km/hr)
Relative velocity = 0 km/hr

So, the ball will appear to be stationary to Bob, and he will not see it moving towards him or away from him. However, if he measures its speed with a radar gun, he will see it moving towards him at 75 km/hr.

Bob Is Coming Toward You at a Speed of 75