Question 286448
first find out how many cm in a km
{{{100}}}cm/m x {{{1000}}} m/km = {{{10^5}}} cm/km
Now how far does the car go in 1 revolution of the wheel?
It goes 1 circumference which is
{{{C = 2*pi*r}}}
{{{C = 2*3.141*21}}}
{{{C = 131.947}}} cm
How far does the car go in 1 min?
{{{600}}} revolutions/min
{{{131.947}}} cm/rev x {{{600}}} rev/min = {{{79168}}} cm/min
Now find this in cm/hr
{{{60}}} min/hr x {{{79168}}} cm/min = {{{4750084.1}}} cm/hr
Now find this in km/hr
{{{4750084.1}}} cm/hr x {{{1/10^5}}} km/cm = {{{47.5}}} km/hr
check my math, though