After how many seconds will the ball hit the ground?

Question

a ball is throw into the air from a platform 32 feet in a tree at the initial velocity of 56 feet per second. After how many seconds will the ball hit the ground?

Answer 1

s(t) = 32 + 56t - 16t² is the equation of motion where the negative term is due to gravity; s(t) is the height after t seconds.

 

32 + 56t - 16t² = 0

 

Divide by 8 => 4 + 7t - 2t² = 0 => (1 + 2t)(4 - t) = 0

 

The one root makes no physical sense and the other t = 4