Question

An autographed baseball rolls off of a 0.76 m high desk and strikes the floor 0.61 m away from the desk. how fast was it rolling on the desk before it fell off? the acceleration of gravity is 9.81 m/s 2 . answer in units of m/s.

Answer 1

d = distance = 0.76 m 
a = acceleration due to gravity = 9.81 m/s^2
u = initial velocity = 0 (as the ball rolls off the table the vertical velocity = 0 
t = time = missing so we need to solve it 

So we use the equation d = ut + 1/2 at², and ever since u is zero, ut is zero and the equation becomes to d = 1/2 at² and this reorders to t = sqrt (2d/a) = 0.39 seconds. 

Since there are no forces performing in the horizontal direction, this means that there is no acceleration in the horizontal direction and consequently the horizontal velocity is persistent.

Velocity = distance/ time.

Horizontal velocity is therefore horizontal distance/time = 0.61 m/0.39s = 1.56 m/s.