Question

A scientist launched an object upward at a speed of 32 ft per second from a height of 240 feet. The height of the object is modeled by the equation h = 240 + 32t – 16t2. After how much time will the object hit the ground? A 3 seconds B 5 seconds C 12 seconds D 20 seconds

Answer 1

B 5 seconds

Explanation:

h = 240 + 32t – 16t^2

When is this equation 0

0 = 240 + 32t – 16t^2

Factor out 16

0 = -16(-15-2t+t^2)

= -16(t^2-2t-15)

What 2 numbers multiply to -15 and add to -2

-5*3 = -15

-5+3 =-2

0 = -16(t-5) (t+3)

Using the zero product property

t-5=0 t+3=0

t=5 t=-3

Since time cannot be negative

t=5 seconds