You are using a gas powered pump to raise 100 kg of water to a height of 100 m. the energy efficiency of the pump is 20%. by what amount has the internal energy of the water and pump changed?

for this problem i first did:

change in potential energy = mgh
change in potential energy = 100 * 9.81 * 100
change in potential energy = 98.1 kj

but i don't know how to use the efficiency

Ais useful when you need a simple machine to you separate two things. a. lever b. screw c. pulley d. wedge

The particle in a two-dimensional well is a useful model for the motion of electrons around the indole ring (3), the conjugated cycle found in the side chain of tryptophan. we may regard indole as a rectangle with sides of length 280 pm and 450 pm, with 10 electrons in the conjugated p system. as in case study 9.1, we assume that in the ground state of the molecule each quantized level is occupied by two electrons. (a) calculate the energy of an electron in the highest occupied level. (b) calculate the frequency of radiation that can induce a transition between the highest occupied and lowest unoccupied levels. 9.27 electrons around the porphine ring (4), the conjugated macrocycle that forms the structural basis of the heme group and the chlorophylls. we may treat the group as a circular ring of radius 440 pm, with 20 electrons in the conjugated system moving along the perimeter of the ring. as in exercise 9.26, assume that in the ground state of the molecule quantized each level is occupied by two electrons. (a) calculate the energy and angular momentum of an electron in the highest occupied level. (b) calculate the frequency of radiation that can induce a transition between the highest occupied and lowest unoccupied levels.

If steel is more dense that lake water, why can a boat float