Pick the best description of energy efficiency.
a. efficiency is equal to the ratio of energy you put in to the energy you get out.
b. efficiency is equal to the ratio of energy you get out to the energy you put in.
c. efficiency is equal to the sum of the energy you put in to the energy you get out.

An engineer designs a roller coaster so that a car travels horizontally for 152 ft, then climbs 137 ft at an angle of 34.0° above the horizontal. it then moves 137 ft at an angle of 48.0° below the horizontal. if we take the initial horizontal motion of the car to be along the +x-axis, what is the car's displacement? (give the magnitude of your answer, in ft, to at least four significant figures and give the direction of your answer in degrees counterclockwise from the +x-axis.)

Under the action of a constant force an object accelerates at 7.8 m/s2. what will the acceleration be if (a) the force is halved? (b) the object's mass is halved? (c) the force and the object's mass are both halved? (d) the force is halved and the object's mass is doubled?

This is for my 8th grade science class, i really don’t understand. can someone me? , lol.