Suppose two children push horizontally, but in exactly opposite directions, on a third child in a wagon. The first child exerts a force of 69.0 N, the second a force of 91.0 N, friction is 15.0 N, and the mass of the third child plus wagon is 23.0 kg.
What is the system of interest if the acceleration of the child in the wagon is to be calculated?

Acar travels along a highway with a velocity of 24 m/s, west. the car exits the highway; and 4.0 s later, its instantaneous velocity is 16 m/s, 45° north of west. what is the magnitude of the average acceleration of the car during the four-second interval?

Acoal-fired plant generates 600 mw of electric power. the plant uses 4.8 x 10^6 kg of coal each day, and the heat of combustion of coal is 3.3x 10^7 j/kg. the steam that drives the turbines is at a temperature of 300° c, and the exhaust water is at 37° c. (a) what is the overall efficiency of the plant for generating electric power? (b) how much thermal energy is exhausted each day? (c) what is the change in entropy of the universe for this heat engine? (d) using the same heat reservoirs, what is the maximum possible (carnot) efficiency for a heat engine?

Mechanical energy is when the amount of kinetic and potential energies added together remains the same. conserved created lost