A fire is lit in a hot air balloon, causing 100 J of heat to flow into the air in the balloon.  While this happens, the air in the balloon expands, doing 70 J of work.  What is its change in internal energy, in Joules?

A 46-kg woman eats a 522 Calorie (522 kcal) jelly doughnut for breakfast. (a) How many joules of energy are the equivalent of one jelly doughnut? 2.19 Your response differs significantly from the correct answer. Rework your solution from the beginning and check each step carefully. J (b) How many steps must the woman climb on a very tall stairway to change the gravitational potential energy of the woman-Earth system by a value equivalent to the food energy in one jelly doughnut? Assume the height of a single stair is 15 cm. 3.22 X Your response differs significantly from the correct answer. Rework your solution from the beginning and check each step carefully. stairs (c) If the human body is only 26% efficient in converting chemical potential energy to mechanical energy, how many steps must the woman climb to work off her breakfast? 8.4 X Your response is off by a multiple of ten. stairs

Air in a balloon does 37 J of work while absorbing 88 J of heat. What is its change in internal energy?

It is important for the body to be able to cool itself even during moderate exercise. Suppose a 70kg man runs on a treadmill for 30min and at a (total) metabolic energy expenditure rate of 1000W. Remembering that the human body has a 25% efficiency, estimate the amount of (mechanical) work done on the treadmill during that time. A) 450kJB)1350kJC)1000kJD)1800kJ