CPM Homework Help : A2C Problem 11-94

Step 1 (a):

Substitute 0 for h.

80t − 16t² = 0

Answer (a):

It is on the ground at 0 and 5 seconds.

Step 2 (a):

Factor the equation.

16t(5 − t) = 0

Hint (b):

When is the height positive?

Answer (b):

D: 0 ≤ t ≤ 5

Hint (c):

At what time will the object be on the ground, not including when it starts?

Answer (c):

5 seconds

Step 1 (d):

16t ² − 80t + 64 = 0

Substitute 64 for h and solve for t.

Step 3 (d):

Factor the equation.

(t − 1)(t − 4)

Step 2 (d):

Simplify.

t ² − 5t + 4

Step 4 (d):

t = 1, 4

Solve for t.

Step 5 (d):

Use these values to find height greater that 64 ft.

Answer (d):

1< t < 4