College Physics Problem 1.9

Tectonic plates are large segments of the Earth’s crust that move slowly. Suppose that one such plate has an average speed of 4.0 cm/year.
(a) What distance does it move in 1.0 s at this speed?
(b) What is its speed in kilometers per million years?


a) We know that the formula for the distance traveled, d, if we are given rate, r, and time, t is given by d=rtimes t.

Therefore, the distance traveled is 

d= frac{4.0cm}{year}times 1 sectimes frac{1 m}{100 cm} times frac{1 year}{362.25 days} times frac{1 day}{3600 s}=1.3times10 ^{-9} m

Therefore, the distance traveled by the tectonic plate is about 1.3times10^{-9} meters.

b) We need to convert 4.0 cm/year to km/My. 

frac{4.0cm}{year}times frac{1m}{100 cm } times frac{1km}{1000 m} times frac{10^{6}year}{1My}=40 km/My

Therefore, the speed of the tectonic plates is 40 km/My.