How can a simple machine (like a ramp) allow a person to raise up a heavier load

Question

How can a simple machine (like a ramp) allow a person to raise up a heavier load than they normally could?

The machine increases the amount of work done

The machine decreases the force needed to move the load

The machine increases the distance over which the work on the load must be done

Both B & C

A, B, & C

QUESTION 2

A typical CFL lightbulb will consume 24 W of electrical power from a wall socket (or 24 J of energy per second). If the CFL produces light that has a power of 20 W (20 J of light energy per second), what is the efficiency of this CFL?

4%

20%

64%

83%

120%

QUESTION 3

If a weightlifter can do 30 reps with a barbell in 1 minute (where each rep does 12 J of work), what is the power of the weightlifter?

6 W

18 W

30 W

42 W

360 W

  

QUESTION 4

If a 40-gram bullet leaves a gun with a velocity of 500 m/s, how much work was done on it by the force from the gun? (Hint: Recall how work and energy are related.)

10 J

40 J

500 J

5,000 J

5 million J

  

QUESTION 5

If a crane lifts a crate that weighs 2,000 N and does a total of 10,000 J of work on the crate, to what maximum height could the crate be lifted?

0.2 m

5 m

50 m

8,000 m

12,000 m

QUESTION 6

A machine can never have an efficiency above 100%.

True

False

  

QUESTION 7

Any object that is falling to the ground is gaining gravitational potential energy.

True

False

QUESTION 8

Any object that is moving MUST have a nonzero kinetic energy.

True

False

QUESTION 9

The total mechanical energy of any object is always conserved.

True

False

  

QUESTION 10

Work is done by objects on forces.

True

False

A.

The machine increases the amount of work done

B.

The machine decreases the force needed to move the load

C.

The machine increases the distance over which the work on the load must be done

D.

Both B & C

E.

A, B, & C

Explanation / Answer

1. both B and C

2. efficiency e = 20/24 = 83 %-------option D

3. power P = W/t = 30*12/60 = 6 Watts-----option A

4. W = 0.5 m v^2   = 0.5* 0.04* 500*500 = 5000J -- option D

5. W = mgh---> h = 10000/(2000) = 5m -option B

6. true

7. false

8. true

9. true

10. true

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