3.4 Work
| Site: | Cowichan Valley School District - Moodle |
| Course: | Science 10 with CSS teacher |
| Book: | 3.4 Work |
| Printed by: | Guest user |
| Date: | Saturday, 26 April 2025, 1:19 PM |
Description
Work & Energy
Work
In physics, work has a specific meaning. If work is to be done on an object, two things must happen: (1) a force must act on the object and (2) the object must move through a distance in the direction of the force.
The amount of work done is equal to the product of the force exerted and the distance over which the force acts on the object.
Since force is measured in newtons (N) and distance in metres (m), work can be measured in N.m. One newton⋅metre is called a joule (J) after James Joule (1818-1889).
Work or Not?
In the following situations, identify whether work is being done (or not).
Example #1:
 |
John is pushing on a huge wall partition. He is sweating and pushing with a big force, but he can't budge it. Is John doing work on the wall? If work is being done, is it converted into potential or kinetic energy? Think about an answer before checking solution. |
Example #2:
 |
David is in training and doing sprints with a parachute. Is David doing work on the parachute during the sprints? If work is being done, is it converted into potential or kinetic energy? Think about an answer before checking solution. |
Example #3:
 |
Sonia is doing a plank for 45 seconds. Is Sonia doing work? If work is being done, is it converted into potential or kinetic energy? Think about an answer before checking solution. |
Example #4:
 |
Carol is bench pressing 85 kg. She does 5 repetitions. Is Carol doing work during her bench pressing? If work is being done, is it converted into potential or kinetic energy? Think about an answer before checking solution. |
Example #5:
 |
Val pulls back a bearing in her new sling shot. Did she do work to get the bearing ready to shoot? If work is being done, is it converted into potential or kinetic energy? Think about an answer before checking solution. |
Example #6:
 |
At the first stage of a roller coaster ride, the roller coaster is pulled up to the top of the first hill. Is there work being done here? If work is being done, is it converted into potential or kinetic energy? Think about an answer before checking solution. |
| Energy in Food |
| One of the mose powerful things about working with energy is that it can be represented in SO many forms. We can even measure the energy within our food. Energy from food is usually measured in joules or calories. |
Calculate Work
In the following situations, calculate the work being done.
Example #1:
 |
John is pushing on a car with a force of 400N. After pushing it 5m, what is the work that John did on the car? Is John's work converted into potential or kinetic energy? Think about an answer before checking solution. |
Example #2:
|
David is in training and doing sprints with a parachute. David pulls with an average force of 150N over the 20m sprints. How much work does David do on the parachute? Is David's work being converted into potential or kinetic energy? Think about an answer before checking solution. |
Example #3:
|
Sonia is doing a plank for 45 seconds. She weighs 400 N and is holding herself up about 0.2 of a meter off the floor. What is the work Sonia is doing? Think about an answer before checking solution. |
Example #4:
|
Val pulls back a bearing in her new sling shot. She pulls it back about 30 cm with an average force of 100N. What is the work that Val does? Is Val's work converted into potential or kinetic energy? Think about an answer before checking solution. |
Force of Gravity
In the previous examples, we were provided with the Force applied.
Sometimes, we can calculate the force ourselves.
For example, the weight of something near the Earth's surface is a simple calculation:
F = mg
where,
- m = the mass of the object (in kg)
- g = 9.8 m/s2 = gravitational constant
- F = the force of gravity (or weight) of the object
Examples
In the following situations, calculate the work being done.
Example #1:
 |
What is the work done in lifting a 50 kg box to a height of 1.5m? Is this work converted into Ek or Ep? Think about an answer before checking solution. |
Example #2:
 |
A rock of mass 4.7 kg is lifted from height 2.1 m to 3.0 m. How much work is done on the rock? Is this work converted into Ek or Ep? Think about an answer before checking solution. |
Example #3:
 |
How much work does a golfer do lifting a 46 g golf ball out of the hole and up to his pocket (0.95 m above the ground)? Is this work converted into Ek or Ep? Think about an answer before checking solution. |
Example #4:
 |
If a person carries a 200 N box from one shelf to another (same height but 3 m away), what was the work done? Is this work converted into Ek or Ep? Think about an answer before checking solution. |
Example #5:
|
At the first stage of a roller coaster ride, the roller coaster is pulled up to the top of the first hill. It climbs 50m with an average force of 20,000N. What is the work being done on the roller coaster? Is the work done being converted into potential or kinetic energy? Think about an answer before checking solution. |
Interviews
What do physicists, technologists, and engineers do? Here's an example.