This is an interesting scenario
You hit your shot, the ball ends up on the floor of your golf car. Can you then proceed to drive your golf cart to a better location for a drop?
Stroke play. Ball in cart.
1) Its your cart. 1 PS, move the cart, drop the ball.
2) It's your fellow competitor's cart, no penalty, move the cart, drop the ball.
3) If you are sharing the cart, it's not moving, regardless if the person you are sharing the cart with is sitting in it, still 1 PS. Move the cart, drop the ball.
4) You are sharing the cart which was being driven by the person you are sharing it with, (the cart was moving when you hit it), no penalty. Drop the ball where the cart was when the ball entered it.
Match Play Ball in Cart
1) It's your cart. Same as 1) in stroke play.
2) Opponent's cart. No penalty, move the cart, drop the ball. As an additional option only in match play you can replay the stroke as another option. You must replay the stroke BEFORE your opponent plays his next stroke, however. Otherwise, you can just proceed as 2) above.
3)Sharing the cart.....same as 3) in stroke play.
4) Sharing but driven by opponent....no penalty. Can replay the stroke as an option.
As discussed, if you are sharing a cart, unless it's being driven (moving) by the other person sharing the cart, everything in it is deemed to be your equipment.......including the guy sitting in it waiting for you to play. So don't hit him. 1 PS.