Which statement about a chemical reaction is true?
it occurs only at low temperatures.
it occurs only at high temperatures.
it occurs whenever a physical change takes place.
it occurs whenever a chemical change takes place.

If you touch a hot light bulb and get burned, that is an example of a. radiation b. convection c. conduction

A100-watt light bulb illuminates a solar cell. the electricity from the solar cell operates a water pump that delivers 1 watt of power. what is the efficiency of the system?

The man of mass m1 and the woman of mass m2 are standing on opposite ends of the platform of mass m0 which moves with negligible friction and is initially at rest with s = 0. the man and woman begin to approach each other. derive an expression for the displacement s of the platform when the two meet in terms of the displacement x1 of the man relative to the platform.