##7.35 cm^2##

The equation for is:

##p=F/A##

The force responsible for providing the pressure in the tyres is the weight of the bicycle plus rider.

##w = mg = 90.0 9.8 = 882 N##

But the weight is distributed across two tyres equally (we assume this). So the actual force involved is:

##F=w/2 = 882/2=441N##

Now rearrange the pressure equation to solve for the contact area:

##A = F/p=(w//2)/p=441/(60010^3)=0.000735 m^2##

The area is small so it might be more convenient to use a prefix i.e. ##cm^2##:

##A=0.000735 (10^2)^2 = 7.35 cm^2##

That is a reasonable value for the area of bicycle tyres in contact with the ground.

When converting areas into a prefix the conversion factor must be squared that’s why I multiplied by ##(10^2)^2## above. The ##10^2## is the conversion factor for centi.

Find out more about prefix conversions here: