Warm-Up Exercise for lecture 9

Due 8:00 am, Tues, Sep 29

Physics 105, Fall 2009

You compress a spring 10 cm from its equilibrium position. Then you compress it another 10 cm. In which step did you do more work?
☐ The first 10 cm
☑ The second 10 cm
☐ Both cases involve the same amount of work.

Switchbacks on mountain roads (consider only work done against gravity):
☐ increase the work needed to go up a mountain
☐ decrease the work needed to go up a mountain
☑ keep the work needed the same

Switchbacks on mountain roads (consider only work done against gravity):
☐ increase the power needed to go up a mountain
☑ decrease the power needed to go up a mountain
☐ keep the power the same

Ralph sees that his car's engine is rated at 100 hp. He thinks, "Cool, this means if I ever get in a tug of war with 90 horses, I will win!" Is he thinking about this correctly? What should you tell him?
That's not quite it. Horsepower has to do with power, not with force. 100 hp means that when the car is going near its maximum speeds, the work put out by the engine per time (against air resistance, mainly) will be equal to the work per time that 100 horses could do (plowing fields, for example). It doesn't mean the car is "stronger" than the horses.