Page 215 - Physics

Work, energy and power

(a) What is the gravitational potential Now, elastic potential energy stored in
energy of the object relative to; the spring is given by,

(i) the table top? 1 kx 2
(ii) the fl oor? 2
(b) Find the work done in lifting the Plugging the values in the above
object from the top of the table to formula,
the ceiling.
1
PE = kx 2
Solution 2
(a) Gravitational potential energy 1
2
(i) At the table top PE = ×(50 N/m)×(0.2 m) =1J
2
h = ,
0
Therefore, PE = 1 J
PE = mgh
= 2 kg × 10 m/s × 0 m = 0 J
Example 9.8
(ii) Relative to the fl oor

h = 1.2 m, Find the elastic potential energy stored
in the spring with k = 100 N/m when
PE = mgh
the spring is compressed by 0.1m.
2
= 2 kg × 10 m/s ×1.2 m
= 24 J Solution
Given: k = 100 N/m and x = 0.1m
(b) d = 2.8 m − 1.2 m = 1.6 m
Now, elastic potential energy stored in
But ΔPE = mgh the spring is given by,

= 2 kg × 10 m/s × (1.6 m)
2
1 2
= 32 J 2 kx
Therefore, the work done = 32 J.
Plugging the values in the above
formula,
Example 9.7 1
P.E = kx 2
Find the elastic potential energy stored 2
in the spring with k = 50 N/m when the 1
2
spring is compressed by 0.2 m. PE = ×(100 N/m)×(0.1 m) = 0.5 J
2
Solution
Given: k = 50 N/m and x = 0.2m Therefore, PE = 0.5 J

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Physics Form 1 Final.indd 209 16/10/2024 20:58