An object is dropped off a 5,000 foot cliff. How long will it ...

[ricki]

An object is dropped off a 5,000 foot cliff. How long will it take the object to fall to the bottom of the cliff, to the nearest tenth of a second? Use the projectile equation h= -16.1t^2+v0t+h0, where h is the height of the projectile after t seconds, v0 is the initial velocity of the projectile and h0 is the initial height of the projectile.

[hummingbird]

Pretty straightforward:

v0 = 0 ft/s because it was dropped
h0 = 5000 ft

so now we have an equation:

h = -16.1t^2 + 0 + 5000

and we want to know the time for when the object reaches the ground (h=0) so:

0 = -16.1t^2 + 5000
t^2 = -5000/-16.1

t=17.622 seconds

[coco]

h= -16.1t^2+v0t+h0

-5000 = -16.1 t^2 +0 +0

t^2 = 310.559

t =17.62 s ----answer

note : -5000 denotes height below zero level