Question

A car slams on its brakes, coming to a complete stop in 4.0 s. The car was traveling south at 60.0 mph. Calculate the acceleration. mi/h/s

Answer 1

The car is decelerating with the magnitude of 0.00416 mi/h².

Or

The car is decelerating with the magnitude of 15 mi/h/s.

Step-by-step explanation:

Given that,

Time = 4.0 sec

Speed = 60.0 mph

We need to calculate the acceleration

Using equation of motion

`v = u+at`

Where, v = final speed

u = initial speed

a = acceleration

t = time

Put the value into the formula

`a= (v-u)/(t)`

`a=(0-60.0)/(4.0*3600)`

`a =-0.00416\ mi/h^2`

We need to calculate the acceleration in mi/h/s

`a = (60.0\ mph)/(4.0\ s)`

`a= -15\ mi/h/s`

Negative sign

Hence, The car is decelerating with the magnitude of 0.00416 mi/h².

Or

The car is decelerating with the magnitude of 15 mi/h/s.

Answer 2

We need to apply the following expression

Vf = Vo + a.t

Where a is the acceleration
t is the time it takes to achieve Speed Vf
And Vo the initial speed

In this problem Vo = 60 miles/hour
Vf = 0 (comes to a stop)
t = 4 seconds

a = -60 [miles/hours] / 4 [s] = -15 miles/hour/second (negative as it goes in the opposite direction)