Question

1. Before driving your excellent convertible, you decide to put the top up (made of flexible material).  After merging onto I-64 you bring the car up to the maximum legal highway speed and maintain a steady cruising rate for a time. During this period, with the wind rushing over the top of the car and the air inside the car perfectly still, you notice that the material over the top of the convertible:

		Doesn't do anything in particular.
		Bends slightly inward towards the interior of the car.
		Bends upward and outward.
		Not enough information to know ahead of time.

2. Explain, in words only, the relationship between work and energy. What's the difference between them?

3. An athlete during training exercises his muscles by pressing firmly and steadily against a wall with a force of 500 N for 5.0 minutes. What is the amount of work the athlete does on the wall during this time, in Joules?

4. A legend about Archimedes claims that the king brought him a crown that was supposed to be solid gold, but the king suspected that it was not entirely gold but had cheaper metals mixed into it. He wanted Archimedes to come up with a way of figuring out if the crown was, indeed, solid gold.  Archimedes pondered on this for a long time until finally one day he was in the bath and a solution came to him. As the story goes, he leaped out of the bath and ran clothes-less through the streets of Athens shouting, "Eureka!", which means "I have found it!" Using concepts from our course, can you think of specific ideas he may have had that led him to realize he could determine the composition of the King's crown?

Answer 1

1) work and energy

scientifically speaking, work is the product of force applied and the displacement produced in any body (object), whereas the energy is the capability of a body to do work.

Both work and energy has same SI units = Joules

2) Force = 500 N

Time = 5 minutes

work done = force*displacement

since displacement = 0

therefore, work done = 0 Joules

3) the archemidies had the idea that every object displaces a liquid whenever the object is immersed in a liquid , and also the amount of liquid displaced is equal to the amount of weight lost by object in the liquid due to the buoyant force. Thus, he came up with the idea, if the crown was made of pure gold, then the amount of liquid displaced would be same as that displaced by pure gold bar.