Table of contents | |
Introduction | |
Using Hooke's Law | |
Exam Tip | |
Solved Example |
Hooke's Law states that a force applied to a spring will cause it to extend by an amount proportional to the force
Look out for unit conversions! Unless the spring constant is given in N/cm, make sure the extension is converted into metres (÷ 100) before substituting values into the Hooke's Law equation
Example: The figure below shows the forces acting on a child who is balancing on a pogo stick.The child and pogo stick are not moving.
The spring constant of the spring on the pogo stick is 4900 N/m. The weight of the child causes the spring to compress elastically from a length of 40 cm to a new length of 33 cm.Calculate the weight of the child.
Step 1: List the known quantities
Spring constant, k = 4900 N/m
Original length = 40 cm
Final length = 33 cmStep 2: Write the relevant equation
F = keStep 3: Calculate the extension, e
e = final length – original length = 40 – 33 = 7 cmStep 4: Convert any units
Since the spring constant is given in N/m, e must be in metres (m)
7 cm = 0.07 mStep 5: Substitute the values into the Hooke's Law equation
F = 4900 × 0.07 = 343 N
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