Help!! I need really quick help with this question!! If a kangaroo jumps from ground level with an initial vertical velocity of 64 feet per second, how long is the kangaroo in the air?

Question

Use the vertical motion model s(t) = -16t² + vt + s where v is the initial velocity, and s is the initial position. If a kangaroo jumps from ground level with an initial vertical velocity of 64 feet per second, how long is the kangaroo in the air?

Answer 1

h = -16t^2 +64t

h' = -32t + 64 = 0

t = 64/32 = 2 second to peak height

double it to get when it hits the ground

t =2(2) = 4 seconds to come back to earth

or set h=0

-16t^2 +64t = 0

-16t(t -4) = 0

t-4=0

t=4 seconds to reach height of zero= when the kangaroo's jump ends in a broken foot or two