Question

A rock is thrown with a horizontal speed of 50 m/s forward from a bridge. The rock reaches the water below 4 seconds later. Let up and forward be considered positive.

(a) What is the horizontal component of the rock's velocity when it reaches the water? (answer should be in m/s)
(b) What is the vertical component of the rock's velocity when it reaches the water? (answer should be in m/s)
(c) What is the speed of the rock when it reaches the water?(answer should be in m/s)
[Use = 10 m/s2]

Answer 1

The horizontal velocity component is CONSTANT. There is no horizontal force so no change in horizontal velocity.

h = Hi - 5 t^2
0 = Hi - 5 (16)
Hi = 80 meters high

v = -10 t = -10 * 4 = about -40 m/s

speed at ground = sqrt( 50^2 + 40^2)