# Warm-Up Exercise for lecture 15

## Due 8:00 am, Tues, Oct 21

Physics 105, Fall 2008

Two people sit on a seesaw. They sit in positions such that the seesaw is balanced in a horizontal position. True/False: The two people must weigh the same amount.
☐ true
☑ false

In order to apply the most torque to a screw, you should:
☑ use a wrench with a long handle
☐ use a wrench with a short handle
☐ there would be no difference

A meterstick is hung from a string attached to its middle, the "50 cm" mark. A rock (1 kg) is tied to the stick at the "0 cm" mark. A second rock, (2 kg)  is also tied to the stick. If the system is balanced, where must the second rock be?
☐ at the 25 cm mark
☐ at the 50 cm mark
☑ at the 75 cm mark
☐ at the 100 cm mark
☐ none of the above

Ralph noticed that both torque and work are obtained by multiplying a force times a distance. He wants to know: how are they different? Do they have the same units? What can you tell Ralph to help him out?

One difference is that work is done on an object over a period of time, whereas torque is basically a force applied to the object at an instant of time. They do have the same units, but represent very different things. Therefore the units of torque are usually written as Nm, whereas the units of energy & work are usually written as J.