It is straightforward to calculate work done and energy changed using the equation when the force is constant.
If the force varies, we can use a graph of force against displacement.
Key Concepts
Work done = force x distance. This is the same as the area under a force-displacement graph.
Use quizzes to practise application of theory.
START QUIZ!
The graph shows the force as a block is pulled along a horizontal friction free surface.
The work done moving 6m = J
The gain in KE = J
The gain in PE = J
Since no friction work done = energy gained by block
Flat surface so no gain in PE
The graph shows how the force acting on a spring varies as it is stretched.
The work done in stretching the spring from 0 to 3 cm = J
The gain in elastic PE = J
Area of triangle = 1/2 base x height.
Must convert cm to m
The graph shows how the force varies as a block is pulled a long a table
The work done by the force from 0 - 2 m is
Count the squares, each one is 1 J
The graph shows the how the force on a block varies as it is pulled along a horizontal frictionless surface starting from rest.
Which of the following statements are true?
The force increases, accelerating the block then changes direction slowing it down.
Not so easy to create in practice but I managed in Algodoo with an increasing thruster then heavy air resistance that was proportional to speed.
How much of Force vs displacement graphs have you understood?
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