Units Dimensions and Conversions

Car companies often boast about the short time it takes their car to accelerate from 0 mph to 60 mph. If a car has a 0-to-60 time of 8.20 seconds, what is its acceleration in m/s/s?

Solution: 3.27 ms^-2

Sketch:

This problem has a slight hitch to it: We are given a speed (mph -- look at the units!) and need an acceleration -- which needs speed / time units.

So, what is the acceleration?

(change in speed) / time = (60mph - 0mph) / 8.20 s

                         = (60 mi/hr) / 8.20 s    

                         = 7.317073171 mi/hr/s

So we need to change the mi to m and the hr to s using

1 mile = 1.61x10³ meters

1 hour = 3600 seconds

So:

We'll use 3 sig figs (assuming that 0 and 60 are very accurate).

Try another problem like this one.

Next Try It Out Problem.

Developed by

Shodor
in cooperation with the Department of Chemistry,
The University of North Carolina at Chapel Hill

Another Problem 2

Question:

Solution: 3.27 ms-2 Sketch:

Solution: 3.27 ms^-2

Sketch: