Kinematics Problem.

[Nenad]

hi guyes, I was wondering if someone could help me with a problem I had on a quiz. The question hes been puzzeling me for some time now.

A ball is thrown upward in an open roof elevator travelling at 10m/s(elevator speed). The balls speed is 20m/s. How much time does it take for the ball to reach the same point it was thrown at?

[Pyrrhus]

You could use galilean transformations to solve this one, the 10m/s of the elevator must be relative to a inertial frame observer, as the 20m/s. Find the speed relative to the elevator, to simplify calculations.

[Doc Al]

A ball is thrown upward in an open roof elevator travelling at 10m/s(elevator speed).
Is the elevator rising or falling? The balls speed is 20m/s.
I assume that's the ball's speed with respect to the earth/elevator shaft.
How much time does it take for the ball to reach the same point it was thrown at?
I assume you mean same point with respect to the elevator car?

Find the position of the elevator car as a function of time. (Constant speed.)
Find the position of the ball as a function of time. (Constant acceleration.)

Set them equal and solve for the time.