Question

An object is thrown up from the top of building 50 m high. it rises to a maximum height of 20 m above the roof.?
a) when does it land on the ground
b) at what velocity does it land?
c) what is its velocity 15m below the roof?

Answer 1

a. h = 50 + 20 = 70 m Above gnd.

V^2 = Vo^2 + g*h = 0
Vo^2 - 9.8*20 = 0
Vo^2 = 196
Vo = 14 m/s. = Initial velocity.

V = Vo + g*Tr = 0
14 - 9.8Tr = 0
9.8Tr = 14
Tr = 1.43 s. = Rise time.

h = 0.5g*t^2 = 70 m.
4.9t^2 = 70
t^2 = 14.3
Tf = 3.78 s. = Fall time.

Tr+Tf = 1.43 + 3.78 = 5.21 s. to reach
gnd.

b. V = Vo + g*Tf
Vo = 0
g = 9.8 m/s^2
Tf = 3.78 s.
Solve for V.

c. V^2 = Vo^2 + 2g*h
Vo = 0
g = 9.8 m/s^2
h = 70-35 = 35 m.
Solve for V.