Question

A car traveling at +30 m/s brakes to exit the highway with an average
acceleration of -3 m/s2. About how long is it before the car slows to +5 m/s?
OA) 5 S
OB) 85
OC) 10 s
OD) 18 s​

Answer 1

Answer:

Approximately 8 seconds (which seems to be Answer B although there is a typo)

Explanation:

Use the formula that defines acceleration of an object as the difference between its final velocity and its initial velocity divided by the time it took to go from one to the other:

$a = \frac{Vf-Vi}{t}$

We use this expression and the values given to solve for the unknown "t" (time):

$a = \frac{Vf-Vi}{t} \\-3 = \frac{5-30}{t} =\frac{-25}{t} \\t= \frac{-25}{-3} = 8.33333333333...$

Given the units of the physical quantities, the answer for t is in seconds. We round it to about 8 seconds.