Describe the relative amounts of potential and kinetic energy for a book in the following situations. a. The book on a high shelf which is 2 meters off the ground.
All energy is in form of potential energy.

b. The book after it has fallen off the 2-meter shelf and is now 1 meter off the ground.
Half of the energy is potential, half is kinetic.

c. The book just before it hits the ground.
All the energy is kinetic.

Aray of light traveling parallel to the principal axis of a concave mirror will be reflected through the mirror's

Consider an ordinary, helium-filled party balloon with a volume of 2.2 ft3. the lifting force on the balloon due to the outside air is the net resultant of the pressure distribution exerted on the exterior surface of the balloon. using this fact, we can derive archimedes’ principle, namely that the upward force on the balloon is equal to the weight of the air displaced by the balloon. assuming that the balloon is at sea level, where the air density is 0.002377 slug/ft3, calculate the maximum weight that can be lifted by the balloon. note: the molecular weight of air is 28.8 and that of helium is 4.

Polly is pushing a box across the floor with a force of 30 n. the force of gravity is –8 n, and the normal force is 8 n. which value could describe the force of friction if polly could not move the box?