Question

Seeing a police officer ahead and not being sure of the speed limit, a driver slows from 65 mi/hr to 55 mi/hr in 4.0 seconds, trying not to make it obvious. What is the car's acceleration?
A 2.5 m/s2

B -2.5 m/s2

C 16 m/s2

D - 16 m/s2

Answer 1

Answer:

$-1.13 m/s^2$

Explanation:

The acceleration of the car is given by:

$a=\frac{v-u}{t}$

where

v is the  final velocity

u is the initial velocity

t is the time

Here we have to convert the velocities from mi/hr to m/s. Keeping in mind that

1 mi = 1609 m

1 h = 3600 s

We get:

$u = 65 mi/h \cdot \frac{1609}{3600}=29.1 m/s\\v = 55 mi/h \cdot \frac{1609}{3600}=24.6 m/s$

While the time interval is

t = 4.0 s

Substituting,

$a=\frac{24.6 - 29.1}{4.0}=-1.13 m/s^2$