Agirl stands on the roof of 55m tall building and throws a baseball
at an angle of 30° above horizontal at an angle of 10m/s.
a. how long the ball is in air.

3.9 seconds

Explanation:

Given:

y₀ = 55 m

y = 0 m

v₀ = 10 sin 30° m/s = 5 m/s

a = -9.8 m/s²

Find: t

y = y₀ + v₀ t + ½ at²

0 m = 55 m + (5 m/s) t + ½ (-9.8 m/s²) t²

0 = 55 + 5t − 4.9t²

4.9t² − 5t − 55 = 0

Solve with quadratic formula:

t = [ -(-5) ± √((-5)² − 4(4.9)(-55)) ] / 2(4.9)

t = (5 ± √1103) / 9.8

t = 3.9

the part of the wave he is travelling on is the crest