Physics 8: HW2 book problems

• 7.E.1: Your body is presently converting chemical potential energy from food into thermal energy at a rate of about 100 J/s, or 100 W. If heat were flowing out of you at a rate of about 200 W, what would happen to your body temperature?
• 7.E.4: You throw a ball into a box and close the lid. You hear the ball bouncing around inside the box as the ball's energy changes from gravitational potential energy to kinetic energy, to elastic potential energy, and so on. If you wait a minute or two, what will have happened to the ball's energy?
• 7.P.1: If a burning log is a black object with a surface area of 0.25 m² and a temperature of 800°C (note: not Kelvin), how much power does it emit as thermal radiation?
• 7.P.2: When you blow air on the log in 7.P.1, its temperature rises to 900°C. How much thermal radiation does it emit now? Why did the 100°C rise make so much difference?
• 7.P.3: If the sun has an emissivity of 1 and a surface temperature of 6000 K, how much power does each 1 m² of its surface emit as thermal radiation?
• 3.P.2: You have another friend who weighs 1000 N. When this friend sits on the chair from Problem 3.P.1, how far does it bend? [3.P.1: Your new designer chair has an S-shaped tubular metal frame that behaves just like a spring. When your friend, who weighs 600 N, sits on the chair, it bends downward 4 cm. What is the spring constant for the chair?]
• 3.P.4: When you stand on a particular trampoline, its springy surface shifts downward 0.12 m. If you bounce on it so that its surface shifts downward 0.30 m, how hard is it pushing up on you?