A girl on a bicycle has a specific amount of kinetic energy at the base of a hill. She then coasts up the hill without pedaling. She comes to a stop at the top of the hill. Why is her potential energy at the top of the hill less than her kinetic energy at the bottom of the hill?

A) The hill did work on the bicycle as she went up the hill.

B) The rest of the energy is stored in the muscles of her body.

C) She still has kinetic energy while stopped on top of the hill.

D) Friction and air resistance created heat on her trip up the hill.

THE ANSWER IS D

Arunner is training for an upcoming marathon by running around a 100-m-diameter circular track at constant speed. let a coordinate system have its origin at the center of the circle with the x-axis pointing east and the y-axis north. the runner starts at (x, y) = (50 m, 0 m) and runs 2.5 times around the track in a clockwise direction.

A15.75-g piece of iron absorbs 1086.75 joules of heat energy, and its temperature changes from 25°c to 175°c. what is the specific heat capacity of iron?

Conventional hot-water heaters consist of a tank of water maintained at a fixed temperature. the hot water is to be used when needed. the drawback is that energy is wasted because the tank loses heat when it is not in use, and you can run out of hot water if you use too much. some utility companies are encouraging the use of on-demand water heaters (also known as flash heaters), which consist of heating units to heat the water as you use it. no water tank is involved, so no heat is wasted. a typical household shower flow rate is 2.50 gal/min (9.46 l/min ) with the tap water being heated from 51.0 ˚f (10.6 ˚c) to 120 ˚f (48.9 ˚c) by the on-demand heater.what rate of heat input (either electrical of from gas) is required to operate such a unit, assuming that all the heat goes into the water?