Question

In a game of football outdoors on a cold day, a player will begin to feel exhausted after using approximately 8.0 × 105 J of internal energy. (a) One player, dressed too lightly for the weather, has to leave the game after losing 6.7 × 105 J of heat. How much work has he done? (b) Another player, wearing clothes that offer better protection against heat loss, is able to remain in the game long enough to do 2.6 × 105 J of work. What is the magnitude of the heat that he has lost?

Answer 1

a) How much work has he done = dW = 1.3 × 105 J

b) What is the magnitude of the heat that he has lost = dQ = -5.4 × 105 J

Explanation:

• From the first law of thermodynamics; dQ = dU + dW

• dU = -8.0 × 105 J

• dQ = -6.7 × 105 J

Hence, work done dW = dQ - dU

dW = -6.7 × 105 J - ( -8.0 × 105 J)

dW = 1.3 × 105 J is the work done by the player

• for heat lost; from dQ = dW + dU

• dU = -8.0 × 105 J and dW = 2.6 × 105 J

• heat lost dQ = 2.6 × 105 J + ( -8.0 × 105 J)

• dQ = -5.4 × 105 J

• The negative is as a result of heat lost by the player