Driving at 75m/s, you hit the brakes on your new car, accelerating at a rate of -20m/s. How long will it take the car to come to rest?

Question

Driving at 75m/s, you hit the brakes on your new car, accelerating at a rate of -20m/s. How long will it take the car to come to rest?

 

Show work (Acceleration or Average Speed)

Answer 1

you can plug it into this equation:

 

final velocity = initial velocity + acceleration x time

in this question:

 

0m/s = 75m/s -20m/s²(time)

subtract 75 m/s from both sides

 

-75m/s= -20m/s²(time)

divide both sides by -20m/s²

 

Time= 3.75s

Answer 2

We use the formula

 

v_F = v_i + at

 

where:

v_F = final velocity

v_i = initial velocity

a = acceleration

t = time

 

What is known:

v_F = 0 m/s

v_i = 75 m/s

a = -20 m/s²

 

What is unknown: t

 

Plug in the known values into the formula to solve for t.  If you get a negative value for t, take the absolute value.  This is because time is always a positive value.

 

Also, -20 m/s²   means that the vehicle is actually slowing down at 20 m/s².