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?

He sees the ball coming at him at 150 km/hr

Explanation:

Relative velocity is the velocity of Object A as it appears to Observer B moving at a particular velocity. For example when you are in a moving car or vehicle on the road other cars appears to be slower than their original Velocity when they are moving in the same direction.

For the case above the the velocity of the ball to bob (the observer) appears to be faster than its original speed because they're moving in opposite directions.

Vr = Vb + Vo

Vr = relative velocity

Vb = velocity of baseball

Vo = velocity of the observer bob

Vr = 75km/hr + 75km/hr

Vr = 150km/hr

Therefore, bob sees the baseball coming at 150km/hr

He sees the ball coming at him at 150 km/hr.

Explanation:

In Newtonian physics, the observer would say that the velocity of the first object is the sum of the two velocities.

Due to the same direction, both velocities will be added.