Everything Science Grade 12

CHAPTER 8. WORK, ENERGY AND POWER 8.4

the forklift exert in holding the crate in place?

SOLUTION

Step 1 : Determine what is given and what is required

We are given:

• mass of crate: m=100 kg


• height that crate is raised: h=8 m


• time taken to raise crate: tr=4 s


• time that crate is held in place: ts=20 s
  We are required to calculate the power exerted.

Step 2 : Determine how to approach the problem

We can use:

P = F

Δx

Δt

to calculate power. Theforce required to raise the crate is equal

to the weight of the crate.

Step 3 : Calculate the power required to raise the crate

P = F

Δx

Δt

= m· g

Δx

Δt

= (100 kg)(9,8 m· s−^2 )

8 m

4 s

= 1 960 W

Step 4 : Calculate the power required to hold the cratein place

While the crate is beingheld in place, there is no displacement.

This means there is no work done on the crate and therefore there

is no power exerted.

Step 5 : Write the final answer

1 960 W of power is exerted to raise the crateand no power is

exerted to hold the cratein place.

Activity: Simple measurements of human power

You can perform various physical activities, forexample lifting measured

weights or climbing a flight of stairs to estimate your output power, usinga stop