High School Physics : Work
Study concepts, example questions & explanations for High School Physics
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Example Questions
Example Question #4 : Work Kinetic Energy Theorem
A 
Use the data given to calculate the kinetic energy of the rocket at the two different velocities. Then find the amount of work done using the following equation:
Kinetic energy of the rocket at the two velocities:
The change in the kinetic energy at the two velocities:
Example Question #5 : Work Kinetic Energy Theorem
A bodybuilder lifts a 
Work is a vector quantity equal to the change in energy in a given direction. Our net work will be equal to product of force and displacement.
We can write this equation in terms of Newton's second law to incorporate our given values.
During its motion the weight travels a distance of 0.5m upward, and then 0.5m downward. Its total distance will be 1.0m, however, we are looking for its displacement. The initial height and final height are equal, making the displacement equal to zero.
The total work will be zero because there was no net displacement.
Example Question #6 : Work Kinetic Energy Theorem
Which of the following is an example of work?
A weightlifter lifts a heavy barbell above his head.
A skier skis down a frictionless hill with no loss in kinetic energy.
A car drives along the road at a constant speed.
A man sits in a chair.
A student types numerous essays for class.
A weightlifter lifts a heavy barbell above his head.
Work is a force times a distance or 
Only one of these has a force times a distance: the weightlifter lifting a weight above his head.
The car moving at a constant velocity has no acceleration and therefore no force.
Typing essays does not require a force times a distance (though it sure feels like work!).
If the skier has no loss in energy, then no work was done, as work is also the measurement of the change in energy.
The man sitting in a chair has a constant velocity of zero, no acceleration, and therefore no force.
Example Question #7 : Work Kinetic Energy Theorem
A 
Known
Unknown
We can use the work kinetic energy theorem to solve this problem. The work done to the object causes a change in kinetic energy.
Work is equal to the force times the displacement over which the force acted.
Therefore
Plug in our variables and solve
Example Question #8 : Work Kinetic Energy Theorem
A 
Work is a force times a distance:
We know the distance that the book needs to travel, but we need to solve for the lifting force required to move it.
There are two forces acting upon the book: the lifting force and gravity. Since the book is moving with a constant velocity, that means the net force will be zero. Mathematically, that would look like this:
We can expand the right side of the equation using Newton's second law:
Use the given mass and value of gravity to solve for the lifting force.
Now that we have the force and the distance, we can solve for the work to lift the book.
This problem can also be solved using energy. Work is equal to the change in potential energy:
While on the ground, the book has zero potential energy. Once back on the shelf, the energy is equal to 
Example Question #9 : Work Kinetic Energy Theorem
Rodrigo pushes a sofa 
We need to know the coefficient of friction of the sofa on the floor to solve
We need to know the mass of the sofa to solve
Work is the product of a net force over a given distance.
In order for there to be work, there must be a net force applied and the object must have a non-zero displacement. In this question we are given the displacement, but we have to solve for the force.
The question only tells us that the couch moves with constant velocity. This tells us that acceleration is zero. If acceleration is zero, then force must also be zero according to Newton's second law.
If the force is zero, then the work is also zero.
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