Question

A(n) 2.6-kg copper block is given an initial speed of 8.0 m/s on a rough horizontal surface. Because of friction, the block finally comes to rest.

(a) If the block absorbs 85% of its initial kinetic energy as internal energy, calculate its increase in temperature. °C

(b) What happens to the remaining energy?

i) It vanishes from the universe.

ii) It becomes chemical energy.

iii) It is so minute that it doesn't factor into the equation.

iv) It is absorbed by the horizontal surface on which the block slides.

Answer 1

The kinetic energy is (1/2)mv²=
0.5 x 2.6kg x 8.0m/s = 10.4J
85% of 10.4J = 8.84J, which is the heat gained.

Q = m c T, so T = Q/m c =
T = 8.84J / (2.6kg x 390) = 0.00872^oC.

(b)

Remaining energy heats the surface and surrounding air. It is absorbed by the horizontal surface on which the block slides