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Physics

The work done by a 1 N force over a 1 m distance is considered to be the unit of
measurement of work.
In the SI system the unit of work is a joule (J). Therefore: 1 J = 1 N · m

Look at this worked example. You move to a new flat and take a 1.5 kg box with toys to put
in the boot of the car at 80 cm height. Calculate the work done.

textbooks nis edu kz
Given SI Solution
m = 1.5 kg F = P = mg
h = 80 cm 0.8 m s = h
А = ?
A = F · s = mg · h
N
A = 1.5 kg · 10 · 0.8 m = 12 J
kg

Answer: А = 12 J

ACT What work is being done in the following images?

1 2 3

INV Explore the relationship between mechanical work and force, using
the system shown in the image on the right:

1. What does the force acting on the block equal at the point at which
it starts to slide across the table? Will the force change if a 100 g load
is placed on the block? What about a 200 g load? Or 300 g?
2. Does the mechanical work depend on the material of the table
surface and the contact area?

3. Analyze and write your results in an appropriate table. Come to a conclusion.

OVER TO YOU!

1. In detail, explain the 2. Ilya Ilyin, a Kazakhstani weightlifter,
forces under the effect lifted a 242 kg bar 2.1 m high at the
of which work is done in world championships, setting a new
the following scenarios: world record. That is a minimum force
of 2420 newtons!
a) a sledge is sliding
down a hill a) How would the work change if Ilya were taller?

b) a stone is falling b) Is it better for a weightlifter to be short or tall? Why?
vertically
3. Compare the work done by a man when he takes the stairs to the
c) a car is slowing down 7th floor and when he uses the lift to get to the same floor. Explain
on a level road your answer.
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