1.Work is only being done when what happens to an object?
A) the object does not move
B) the object disappears without explanation
C) it moves in the same direction as the force
D) The object moves in the opposite direction of the force

2.Ben and Jerry, arch rivals, decide to have a weight lifting contest during PE. Ready, set, go! Ben and Jerry both lift a 250 kg barbell 10 times over their heads. They are approximately the same height and lift the barbell the same distance in the air. It takes Ben 5 seconds to complete 10 lifts; it takes Jerry 25 seconds to complete his 10 lifts.
Which statement is MOST accurate regarding the weightlifting contest?
A) Ben did more work than Jerry.
B) Ben has more power than Jerry.
C) Ben and Jerry have the same power.
D) Ben does more work and is more powerful than Jerry.

3.Which energy source can be found on the electromagnetic spectrum?
A) sound energy
B) chemical energy
C) UV light energy
D) mechanical energy

4. Sam blew up a balloon and rubbed it on his head. Then he stuck the balloon on the wall. This was all the result of electrostatics or the transfer of charge. The appearance of negative charge on a balloon is the result of its gaining electrons. And these electrons must come from somewhere; in this case, from Sam's hair. Electrons are transferred in any charging process. In the case of charging by friction, they are transferred between the two objects being rubbed together. Prior to the charging, both objects are electrically neutral and the situation obeys the law of conservation of charge. How does the law of conservation of charge explain Sam and his balloon?
A) Friction creates charge that collected on the balloon.
B) The balloon gained electrons; Sam's hair gained protons.
C) If the balloon acquires charge, Sam's hair loses charge.
D) The net charge before is zero; the net charge after is negative.

As we see from the formula, when d=0 (the object does not move), then W=0 (no work done). While we have work done if the object is moving. In particular, we have two situations:

- The object moves in the same direction as the force: [tex]\theta=0^{\circ}[/tex], so [tex]cos \theta= 1[/tex] and the work done is positive

- The object moves in the opposite direction of the force: [tex]\theta=180^{\circ}[/tex], so [tex]cos \theta= -1[/tex] and the work done is negative

2. B) Ben has more power than Jerry.

Power is defined as:

[tex]P=\frac{W}{t}[/tex] (1)

where

W is the work done

t is the time taken

Work is the product of force and displacement. Since Ben and Jerry lift the same mass (250 kg), they apply the same force, and since they lift the barbell the same distance in air the same number of times (10), the displacement is also the same: so, they did the same work.

However, Ben did it in less time (5 s) then Jerry (25 s): looking at eq.(1), we see that less time means more power, so Ben has more power than Jerry.

3. C) UV light energy

The electromagnetic spectrum is the classification of all electromagnetic waves according to their different wavelength.

From shortest to longest wavelength, we have:

Gamma rays

X-rays

UV (ultraviolet)

Visible light

Infrared radiation

Microwaves

Radio waves

So, we see that UV light energy (ultraviolet radiation) is a type of electromagnetic waves.

4. C) If the balloon acquires charge, Sam's hair loses charge

The law of conservation of charge applied to this case states that the total charge on Sam hair and the balloon before must be equal to the total charge after: no charge can be created or destroyed in the process, but only moved from one object to the other.

In this example, Sam rubs the balloon on his head: electrons are transferred from Sam's hair to the balloon's surface. Therefore, we can say that the balloon has acquired negative charge, while Sam's hair has lost negative charge.