#### Question

# Energy and Power Physics Questions?

1. If you push against a wall, are you doing any work on the wall?

? a. Yes, the effort tires you out.

? b. Yes, you are applying force to the wall.

? c. No, the wall doesn't move.

? d. No, you don't move.

2. A person does 45 J of work by dragging a 22 kg box 3.7 m across the floor. How much force does this require?

? a. 0.55 N

? b. 2.04 N

? c. 12.2 N

? d. 58 N

Questions 4 and 5

A 0.32 kg ball is thrown with a speed of 11.5 m/s.

4. How much kinetic energy does the ball have?

? a. 21.2 J

? b. 42.3 J

? c. 1.84 J

? d. 35.9 J

5. How much work would be needed to stop the ball?

? a. 1.84 J

? b. 21.2 J

? c. 35.9 J

? d. 42.3 J

Can you please help me? i totally forgot how to do them!?

#### Answers

1) C Work = Force * Distance..the wall doesn't move, so distance = 0 so there is no work

2) C W = F*d ; F = W/d = 45/3.7 = 12.2N

4) A E = .5mv2 = 21.2 J

5) B Stopping a moving object is the opposite of getting it to move, therefore it would be the same as number 4) 21.2 J

1: C because work is only done when a force is applied and it moves a certain distance in the same direction

2: A because: Work Done = Force x Distance

Force = mass x R

F = 22R

45 = 22R x 3.7

R = 0.5528...

4: A

KE = 1/2 mv^2

KE = 1/2 x 0.32 x (11.5^2)

KE = 21.16

KE = 21.2 (3sf)

5: B

WD = change in kinetic energy

WD = 1/2mv^2 - 1/2mu^2

v = 0 when ball stops, u = 11.5

WD = 0 - (1/2 x 0.32 x 11.5^2)

WD = 21.2