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Question

A 2.8kg copper is block is given an initial speed of 4.5m/s on a rough horizontal surface. Because of friction, the block finally comes to reset.

If the block absorbs 85% of its kinetic energy as internal enery, calculate incre in temperature in Celsius.

What happens to the remaining energy?

Answer 1

Its initial KE is 1/2 mv^2

It abosrbs 0.85 of it, ie absorbs 0.4 mv^2

= m*cp* ΔT

ΔT = 0.425 v^2 / cp

plug in values

Answer 2

The total energy of the block was:

E = mv2 / 2 = 28.35 J

85% of this is used to heat the block itself, that gives 24.1 J.

To calculate temperature change, use the equation:

mass * specific heat capacity * temperature change = energy

Specific heat capacity for copper is 385 J/kgK, so:

2.8 * 385 * dT = 24.1

This gives a temperature change of 0.022 Celsius.

The remaining energy was absorbed by the surface (as heat).