A physics student standing on the edge of a cliff throws a stone vertically downward with an initial speed of 10.0 m/s. The instant before the stone hits the ground below, it is traveling at a speed of 30.0 m/s. If the physics student were to throw the rock horizontally outward from the cliff instead, with the same initial speed of 10.0 m/s, what is the magnitude of the velocity of the stone just before it hits the ground?
A)10.0 m/s
B)20.0 m/s
C)30.0 m/s
D)40.0 m/s
E)The height of the cliff must be specified to answer this question.

Question

Quizplus · Accepted Answer

The vertical component of the stone's velocity will still be the same as in the first situation (10.0 m/s downward at impact). However, in the second situation, there will also be a horizontal component to the stone's velocity due to the initial horizontal throw. This horizontal component will not affect the time it takes for the stone to hit the ground, and thus will not affect the vertical component of the velocity at impact. Therefore, the total velocity just before impact will be a combination of the initial horizontal velocity (10.0 m/s) and the final vertical velocity (30.0 m/s downward). Using the Pythagorean theorem, the magnitude of this total velocity is: sqrt[(10.0 m/s)^2 + (30.0 m/s)^2] = 31.6 m/s, which is closest to choice C (30.0 m/s).

A Physics Student Standing on the Edge of a Cliff