Question

According to the law of conservation of energy, when a lawnmower uses 750 J of chemical energy from gasoline, how much of this energy will be transformed into mechanical, sound, or heat energy?

Answer 1

Since the energy is conserved, it's not lost, it's conserved. so the 750J of chem should go into cutting the grass, making a noise whilst doing so, and getting warm whilst doing so. How much into which is presumably decided by the (efficient ?) design of the machine.

Answer 2

energy is neither created nor destroyed

E in = E out
750 J in so 750 J out