Question

a girl throws a ball vertically upward with a speed of 20 ft/sec from the roof of a building 60 ft high.(a)how long will it take the ball to reach the ground? (b)what will its speed be when it strikes the ground?

Answer 1

a. V = Vo + g*Tr = 0, Tr = -Vo/g = -20/-32 = 0.625 s. = Rise time.

Tf = Tr = 0.625 s. = Fall time from max ht. to top of bldg.

h = Vo*T + 0.5g*T^2. h = 60 Ft., Vo = 20 Ft/s, g = 32 Ft/s^2, T = ?.

Tr+Tf+T = Time to reach gnd.

b. V^2 = Vo^2 + 2g*h. Vo = 20 Ft/s, g = 32 Ft/s^2, h = 60 Ft., V = ?.