Charles' law explains which of these phenomena?
a. why a balloon deflates when the air around it cools
b. why solids require heat in order to change into gases
c. why the pressure of a gas increases when volume decreases
d. why some gases only react with each other at high temperatures

As you are trying to move a heavy box of mass m, you realize that it is too heavy for you to lift by yourself. there is no one around to , so you attach an ideal pulley to the box and a massless rope to the ceiling, which you wrap around the pulley. you pull up on the rope to lift the box. use g for the magnitude of the acceleration due to gravity and neglect friction forces. once you have pulled hard enough to start the box moving upward, what is the magnitude f of the upward force you must apply to the rope to start raising the box with constant velocity? express the magnitude of the force in terms of m, the mass of the box.

Aperson walks first at a constant speed of 4.89 m/s along a straight line from point a to point b and then back along the line from b to a at a constant speed of 2.95 m/s. what is the average speed over the entire trip?

Matter is needed to transfer thermal energy bya. conductionb. convectionc. radiation d. both a & b.