Question

A ball rolls off the edge of a horizontal roof at 10 m/s. 2 seconds later, the speed of the ball will be? a. 10 m/s b. 19.6m/s c. 29.6 m/s d.22 m/s ...?

Answer 1

The ball rolls horizontally thus it is not affected by the gravitational acceleration. We assume that velocity is constant since we are not given acceleration. Therefore, acceleration is zero. The speed of the ball after 2 seconds will still be the same given we have a constant velocity system. Option A is the answer.

Answer 2

Answer:

d). 22 m/s

Explanation:

Initial horizontal speed of the ball is in x direction

so we have

$v_x = 10 m/s$

now it rolls off the edge and comes into the air. So after that it will start falling down due to gravity and still continue to move in horizontal direction with constant speed.

so after t = 2 s the speed in x direction will remains the same

speed in y direction is given as

$v_f = v_i + at$

$v_f = 0 + (9.81)(2)$

$v_y = 19.62 m/s$

so net speed of the ball is given as

$v^2 = v_y^2 + v_x^2$

$v^2 = 10^2 + 19.62^2$

$v = 22 m/s$