Unit 3: Principles of Mechanical Engineering
LO5: Understand principles of dynamic systems
Work done and Energy
Learner activity sheet
Activity 1
Think about the following problem: a trolley of mass 10 kg starts from rest at the bottom of a smooth
slope at 30o to the horizontal. If a force of 250N propels the body up the slope find its velocity after it has
travelled a distance of 30m.
Step One: Draw a diagram to represent the problem.
Step Two: Calculate the work done by the propelling force (work done = F  d)
Step Three: Taking the bottom of the slope as the datum point find the change in potential energy of the
trolley when it has travelled 30m up the slope. (take g = 10 m/s2)
Step Four: Write down the kinetic energy of the trolley in terms of the unknown velocity v m/s
Step Five: Using the principal that the work done by the propelling force is equal to the total change in
energy of the body find the velocity of the trolley at the 30 m point.
Step Six: Check the result you found in step five by resolving forces and applying the constant
acceleration formulae.
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