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Physics

ACT Calculate the pressure on the road exerted by a truck travelling along a city street,
bearing a load of 30 tonnes. The area of the vehicle’s wheels in contact with the road
2
surface equals 0.5 m .

Given SI Solution
m = 30 tonnes 30 000 kg F mg
p = p =
S s
textbooks nis edu kz
N
S = 0.5 m 2 F = P 30 000 kg ∙ 9.8 kg
p = ≈ 600 000 Pa = 600 kPa
P = ? P = mg 0.5 m 2

Answer: р = 600 kPa

INV Explore the pressure of solids

Your first challenge is to calculate the pressure exerted by different regular-shaped objects
on different-sized surfaces. The next challenge is to calculate the pressure you exert on
both your feet when standing up. Think about it and plan how you will go about this. How
does the pressure change when you stand on one foot? How is it different from when you
are sitting on your chair?

EXT Your friends are going on an expedition to Greenland and they are worried about
trekking along glaciers with potential crevasses. Write a letter to your friends explaining
the science behind what they should do in order to reduce their risk of falling through
the snow.

OVER TO YOU!

1. How does the pressure of a truck on the road change if it is
loaded with sand of equal weight to the truck?

2. Calculate and compare the pressure a man makes on the ground:

а) while walking A 6.7 tonne tractor exerts 4700 Pa
pressure on the ground
b) standing on two feet at rest

The man weighs 500 N and the area of the sole of one shoe is 200 cm .
2
3. When a shark bites, the pressure it exerts reaches a magnitude
of 3≥10 Pa . What is the force exerted by the shark’s teeth
8
if 2≥10 m of skin surface is damaged?
2
-6
A needle exerts 10 Pa pressure on
8
EXT a piece of cloth
1. Calculate the contact area between the tractor tracks and the
ground if the mass of the tractor is 6.7 tonnes and the tractor exerts
4700 Pa pressure on the ground.

8
2. A needle exerts 10 Pa pressure on a piece of cloth and a bee exerts
10
3·10 Pa pressure with its sting. How many times thinner is a bee
sting than a needle-point, assuming that the forces exerted by the
A bee exerts 3·10 Pa pressure
10
needle and the bee are equal? with its sting
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