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Drills on Work, Energy and Power

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Drills on Work, Energy and Power

1. A motor does 5,000 joules of work in 20s. What is the power of the motor?

Given: W = 5,000 J, t = 20s

Required: P = ?

Sol’n: P =

P =

P =

P = 250

P = 250 W

2. A machine does 1,500 joules of work in 30s . What is the power of this machine?

Given: W = 1,500 J, t = 30s

Required: P = ?

Sol’n: P =

P =

P =

P = 50

P = 50 W

3. A toaster oven uses 67,500 joules of energy in 45 seconds to toast a piece of bread. What is the power of the oven?

Given: W = 67,500 J, t = 45s

Required: P = ?

Sol’n: P =

P =

P =

P = 1,500

P = 1,500 W

4. A horse moves a sleigh 1.00 kilometer by applying a horizontal 2,000-newton force on its harness for 2,500 seconds. What is the power of the horse?

Given: F = 2,000 N, d = 1,000m, t = 2,500s

Required: P = ?

Sol’n: P =

P =

P =

P = 800

P = 800 W

5. Suppose a force of 100 Newtons is used to push an object a distance of 5 meters in 15 seconds. Find the work done and the power for this situation.

Given: F = 100 N, d = 5m, t = 15s

Required: W = ?, P = ?

Sol’n: W = Fd

= (100N) (5m)

= 500 J

P =

P =

P = 33.33 W

6. Emily’s vacuum cleaner has a power rating of 200 watts. If the vacuum cleaner does 360,000 joules of work, how long did Emily spend vacuuming?

Given: P = 200 W, W = 360,000 J

Required: t = ?

Sol’n: P =

t =

t =

t = 1,800 s

7. A force of 100 newtons is used to move an object a distance of 15 meters with a power of 25 watts. Find the work done and the time it takes to do the work.

Given: F = 100 N, d = 15m, P = 25 W

Required: W = ?, t = ?

Sol’n: W = Fd

= 100 N (15m)

= 1500 J

t =

t =

8. What is the power of cart having a mass of 25kg and has an acceleration of 30m/ in a period of 30s covering a distance of 100m?

Given: m = 2,500kg, a = 30m/, t = 30s, d= 100m

Required: P = ?

Sol’n: F = ma

= 25kg (30m/)

= 750 N

W = Fd

= 750 N (100m) = 75,000 J

P = =