Question

You are sitting in a car going 20 m/s relative to the ground and decide to throw a ball backwards with a velocity of 4m/s relative to your car. A person in another car behind you sees the ball moving towards him with a velocity of 2.50 m/s relative to his car. What is the velocity of the second car?

My Work:
20/4 = x/2.5
x = 12.5

Is this correct?

Answer 1

suppose an observer were sitting still directly behind you. He would see the ball receding at 20-4 = 16 m/s.

Instead, he sees the ball approaching at 2.5 m/s. So, his velocity is 16+2.5 = 18.5 m/s in your direction.

What's with the ratios? We're not talking about casting shadows here.

Answer 2

oooo I see thank you so much, I just figured that the ratio of the car1 to the ball would equal the ratio of the car2 to the ball for some reason but this makes so much sense ! much appreciated!!!