Jay bought a toy car. to make the car move, he must turn a key attached to a spring. turning the key winds the spring tight. the toy car moves when the key is released and the spring unwinds. what’s the main transformation of energy in this example?

Elastic potential energy into kinetic energy

Explanation:

Initially the energy is stored inside the spring, which is compressed. This form of energy is called elastic potential energy, and its formula is

where k is the spring constant, which gives the 'strength' of the spring, while x is the compression/stretching of the spring with respect to its equilibrium position.

When the spring unwinds, it returns to its equilibrium position, so x becomes zero and the potential energy converts into another form of energy, which is related to the motion of the car (in fact, the car starts moving). This form of energy is called kinetic energy, and its formula is

where m is the mass of the car and v is its speed.