Question

The top speed of a wildebeest is 64 km/h and the top speed of a zebra is 64.4 km/h. How much faster is a zebra in feet per second? 1 km = 0.62137 miles. Round your answer to the nearest hundredths

Answer 1

The zebra is 0.36ft/sec faster.

This is dimensional analysis.  We set up ratios to help us solve this:

Wildebeest:
$\frac{64\textkm}{1\text{hr}}\times\frac{1\text{hr}}{60\text{min}}=\frac{64\text{km}}{60\text{min}} \times \frac{1\text{min}}{60\text{sec}}=\frac{64\text{km}}{3600\text{sec}} \\ \\\frac{64\text{km}}{3600\text{sec}}\times \frac{0.62137\text{mi}}{1\text{km}} =\frac{39.76768\text{mi}}{3600\text{sec}}\times \frac{5280\text{ft}}{1\text{mi}} =\frac{209973.3504\text{ft}}{3600\text{sec}}\approx 58.33\text{ft/sec}$

Zebra:
$\frac{64.4\text{km}}{1\text{hr}}\times \frac{1\text{hr}}{60\text{mi}}=\frac{64.4\text{km}}{60\text{min}} \times \frac{1\text{min}}{60\text{sec}}=\frac{64.4\text{km}}{3600\text{sec}} \times \frac{0.62137\text{mi}}{1\text{km}} \\ \\=\frac{40.016228\text{mi}}{3600\text{sec}}\times \frac{5280\text{ft}}{1\text{mi}}=\frac{211285.6838\text{ft}}{3600\text{sec}}\approx 58.69\text{ft/sec}$

The difference is found by subtracting them:
58.69 ft/sec - 58.33 ft/sec = 0.36 ft/sec difference.

Answer 2

The first thing we must do is subtract both speeds.
 We have then:
 64.4 km / h - 64.0 km / h = 0.40 km / h
 We now change units taking into account the following conversions:
 1h = 3600s
 1km = 3280.84 feets
 We have then:
 0.40 * (3280.84 / 3600) = 0.364537778 feet / s
 Answer: 
 a zebra is faster 0.364537778 in feet per second