Force and Extension
Q1.
Figure 1 shows an exercise device called a chest expander. The three springs are identical.
Figure 1
 
A person pulls outwards on the handles and does work to stretch the springs.
(a)     Complete the following sentence.
When the springs are stretched ___________ ___________ energy is stored in the springs.
(1)
(b)     Figure 2 shows how the extension of a single spring from the chest expander depends on the force acting on the spring.
Figure 2
 
(i)      How can you tell, from Figure 2, that the limit of proportionality of the spring has not been exceeded?
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(1)
(ii)     Use data from Figure 2 to calculate the spring constant of the spring.
Give the unit.
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Spring constant = ___________ Unit ___________
(3)
(iii)     Three identical resistors joined in parallel in an electrical circuit share the total current in the circuit.
In a similar way, the three springs in the chest expander share the total force exerted.
By considering this similarity, use Figure 2 to determine the total force exerted on the chest expander when each spring is stretched by 0.25 m.
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Total force = ___________ N
(2)
(c)     The student in Figure 3 is doing an exercise called a chin-up.
Figure 3
 
Each time the student does one chin-up he lifts his body 0.40 m vertically upwards.
The mass of the student is 65 kg.
The student is able to do 12 chin-ups in 60 seconds.
Calculate the power developed by the student.
Gravitational field strength = 10 N/kg
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Power = ___________ W
(3)
(Total 10 marks)