Question

The reflectors in light houses are used to project the light of the lighthouse out to sea had to be rotated at a certain speed. This rotation of the light gave the lighthouses their distinctive flashing patterns. Each lighthouse has a different pattern so sailors could identify which lighthouse they were approaching. Lighthouses are still used today by sailors as a secondary source of navigation.

The rotation of the beam was achieved through the use of a clockwork mechanism. The clockwork was driven by a heavy 25 kg weight (OSHA recommends that lifting loads heavier than 50 pounds (22.7 kg) will increase the risk of injury but this was before OSHA’s day) that was attached to a cable that wound around a horizontal drum and then through a clockwork mechanism. The weights in the Hatteras Lighthouse ascended and descended inside the center of the tower, guided by cables extending down from the top of the tower.

The weight had to fall at a specified rate to ensure the proper rotation speed of the light. The weight was released from the top to the lighthouse, and over 2.5 hours the weight fell through a distance of 61 m to the floor of the lighthouse. As the weight fell downward it turned the clockwork mechanism causing the lighthouses beam to rotate. The only downside to this situation is that when the weight reached the bottom of the lighthouse, the lighthouse keeper would have to manually return the weight to the top of the tower.

a,) How much work does the keeper have to do to return the weight to the top of the tower?

15,000 Nm

30,000 Nm

23,000 Nm

18,000 Nm

b.) How much work does gravity do in moving the weight downward?

23,000 Nm

30,000 Nm

15,000 Nm

18,000 Nm

c.) How much power is generated by the weight during one trip of the weight from the top to the bottom?

1.4 W

0.6 W

1.7 W

2.3 W

d.) How much power is required to lift the weight from the bottom to the top of the lighthouse? Assume our lighthouse keeper is in excellent shape from performing this task almost 10 times a day and can cover the distance in 5 minutes.

250 W

50 W

3000 W

3 W

e.) What is the potential energy of the weight mechanism at the lighthouse?

30,000 Nm

23,000 Nm

15,000 Nm

18,000 Nm

Answer 1