The current theory of the structure of the earth, called plate tectonics, tells us what the continents are in constant motion. assume that the north american continent can be represented by a slab of rock 4700km on a side and 37km deep and that the rock has an average mass density of 2720kg/m^3. the continent is moving at the rate of about 4.6cm/year. a) what is the mass of the continent. b) what is the kinetic energy of the continent?

A) We need to first determine the volume of the continent and then mass would be = Volume x density

Volume = 4.7 x 10^6 m x 4.7 x 10^6 m x 37 x 10^3m

= 817 x 10^15 cubic meter

Mass = V x density

= 817 x 10^15 cubic meter x 2720kg/m^3

= 2.2 x 10^21 Kg

B)

Kinetic Energy = ½mV²

= ½ x 2.2 x 10^21 Kg x ( 4.6cm/year. x 1m/100cm x 1yr/365.24day x 1day/24hr x 1hr/3600s)²

= 2340 J

acceleration = (change in speed) / (time for the change)

change in speed = (20-120)= -100 m/s.

1.5 min = 90 sec

acceleration = -100/90 = -1.11 m/s^2.

we don't care about the 150kg or the 2,500 meters. they don't make any difference.

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