Where will a rock hit the ground if you drop it out a moving vehicle?

A rock dropped from a car window initially moves forward as the same speed as the car and falls downwards due to gravitational attraction. The forward speed falls off from the air resistance. This rate of speed reduction depends on the mass and density of the rock and the initial air velocity. For simplicity consider the case of dropping the rock in a vacuum (no air), or that the rock is so large that its momentum and inertia reduce the reduction of its forward speed only slightly while the rock is falling.

To the observer in the car w the rock then falls down from the point dropped maintaining its forward speed.

The rock accelerates downward at 32 ft/sec² until it contacts the road some distance "d" below it. Using the expression:

d = vt + (1/2)at²

where d is distance travelled downward, v is starting downward velocity, a is acceleration of gravity, and t is time. It is possible to calculate "t". It is just as easy to time the fall of the rock by experimentation.

The forward movement of the rock lasts for time "t". It was moving at some forward speed "v". It travels
d = vt . Where d is distance travelled forward, v is starting forward velocity, and t is time.

The rock lands under the hand that dropped it at distance "d" down the road.

First answer by Woodwose. Last edit by Woodwose. Contributor trust: 223 [recommend contributor]. Question popularity: 10 [recommend question]