Page 108 - Physics

Physics for Secondary Schools

Example 5.3 Solution
Given data:
Calculate the resulting buoyant force, if
−3
a steel ball of radius 6 cm is immersed Volume of blood (V) = 5.3 × 10 m 3
in water. Assume density of water is
1 000 kg/m and acceleration due to Density of blood ρ ( ) =1060 kg/m 3
3
gravity is 10 N/kg.
Recall, w = mg , where m = ρV
Solution
Given data: w = ρV ( ) g = ρVg

Radius of steel ball = 6 cm = 0.06 m = 1060 kg/m × 5.3 × 10 m × 10 N/kg
3
3
−3
Density of water, ρ = 1 000 kg/m 3 = 56.18 N
Acceleration due to gravity, g = 10 N/kg Therefore the weight of the blood is
56.18 N.
4
Volume of steel ball, V = πr 3
3 Exercise 5.1
4
V = π 0.06) 3
(
3 1. (a) Explain the following terms in
relation to the concept of
−4
=9.04 × 10 m 3 sinking and fl oating.
We know that, (i) Buoyancy.
The magnitude of upthrust U ( ) (ii) Apparent weight.
B
(
= weight w = mg) of a displaced water. (iii) Actual weight.
B
(b) How is the apparent weight of
Then, an object in a fl uid related to its
U = ρV ( ) g actual weight in air?
B
2. An aluminium cube has a volume of
3
= 1 000 kg/m × 9.04 × 10 m × 10 N/kg 800 cm . If it is totally immersed in
−4
3
3
= 9.04 N water, calculate the upthrust acting
on it. Assume density of water is
3
∴ The magnitude of upthrust is 9.04 N. 1 000 kg/m and acceleration due to
gravity is 10 N/kg.
3. An iron piece of mass 360 g and a
Example 5.4 density of 7.8 g/cm is suspended
3
A man whose weight is 690 N contains by a rope so that it is partially
3
−3
5.3 × 10 m of blood. Calculate the submerged (halfway) in oil of density
3
weight of the blood if its density is 0.9 g/cm . Find the tension in the
1 060 kg/m . string.
3
102
Student’s Book Form One

Physics Form 1 Final.indd 102 16/10/2024 20:56