Question

If a car has tires with a radius of 1.5 ft and the tires are spinning at 840 rpm (revolutions per

minute), how fast is the car traveling in mph?
[There are 5280 feet in 1 mile) Round your final answer to 2 decimal places.

Answer 1

89·98 mph

Explanation:

First, we get the circumference of the tires:

Circumference =
`\pi` × (radius × 2)

Circumference = 3.142 × (1·5 × 2)

Circumference = 3·142 × 3

Circumference = 9·426 ft

The circumference of the tire is equal to one round.

1 round = 9·426 ft

840 rounds = ?

We cross multiply to get the length that the tires would cover in a minute

= 840 × 9·426

1

1 minute = 7917·84 ft

60 minutes = ?

60 × 7917·84

1

= 475070·4 ft

5280 feet = 1 mile

475070·4 feet = ?

475070·4 × 1

5280

475070·4 ÷ 5280 = speed of the car in mph

89·97545

Round this off to 2 decimal places...

= 89·98 mph

hope this helps! =)