Question

An object falls from a height of 400 feet. Its height, h, in feet is given by the equation where t is the time in seconds the object has fallen. How many seconds will it take for the object to reach the ground?

Answer 1

Option B is correct, i.e. t = 5 seconds.

Explanation:

Given the equation of height of object is h = -16t² + 400.

When it touches the ground, the height of object would be ZERO.

So the equation becomes:-

0 = -16t² + 400.

16t² = 400

t² = 400/16

t² = 25

t = √25

t = ±5

Since, t is the time and time can not be negative value.

Hence, option B is correct, i.e. t = 5 seconds.