Question

A stuffed toy with a mass of 0.900 kilograms sits on the edge of a bed at a height of 0.830 meters. If the toy falls off the bed, what will its mechanical energy be at a height of 0.500 meters? (Ignore frictional effects.)

A) 0.0 J
B) 3.6 J
C) 7.3 J
D) 10.9 J

Answer 1

Answer: option C) 7.3 J

Justification:

The principle behind this question is the conservation of the mechanical energy.

The mechanical energy that is the sum of gravitational potential energy and kinetic energy.

While the toy falls down it loses gravitational potential energy and gains velocity (kinetic energy). The amount of gravitaional potential energy lost is the same amount of kinetic energy gained, so the total mechanical energy is conserved.

Therefore, you just must calculate the initial potential energy of the toy, because at the begining there is not kinetic energy (the toy is at rest).

The calculation is: Meechanical energy = potential energy + kinetic energy = m*g*h + (1/2)m*v^2 = 0.9 kg * 9.8 m/s^2 * 0.830m + 0 = 7.32 joules.

So, the answer is the option C) 7.3J