## GED Practice

### GED Science review: Work and Power

Questions:

Directions: Write the answer to each question.

Question 1 refer to the following passage.

Energy is the capacity to do work. When a force acts upon an object to cause it to move (or be displaced), it is said that work is done upon the object. There are three key ingredients to work: force, displacement, and cause. In order for a force to qualify as having done work on an object, there must be a displacement, and the force must cause the displacement. Good examples of work can be observed in everyday life. A man pushing a grocery cart down the aisle of a grocery store. a student lifting a backpack full of books onto her shoulder, a basket ball player shooting the ball, and an athlete throwing the shooting the ball, and an athlete throwing the shot-put are all common examples of work.

1. Suppose you push against a wall until you become exhausted. In this situation, work
• is completed because you reached exhaustion.
• is completed because you applied a force to the wall.
• is not completed because your force did not move the wall.
• is not completed because you did not push for a long enough period.
2. Power is the rate at which work is done. A more powerful machine may be able to complete the same amount of work as a less powerful machine, but it will complete the work faster. Some friends were arguing about whose pickup truck has the most power. What kind of experiment could be done to settle the argument?
• Each truck should try to tow heavier and heavier loads.
• Each truck should be driven through an obstacle course.
• Each truck should be driven until it completely runs out of gas.
• The net, or total, work done by a net force acting on an object is equal to the change in the kinetic energy of the object. This important relationship is known as the work-energy theorem. As an equation, it can be written
Wnet = ∆KE
where Wnet is the net work and ∆KE is the change in kinetic energy. When you use this theorem, you must include all the forces that do work on the object. You can also calculate the net
Wnet = Fnetd
where Wnet is the net work, Fnet is the net force, and d is the distance the object travels.
• Each truck should be timed carrying the same load for the same distance.

Question 3 and 4 refer to the following passage.

3. A car accelerates from rest under the action of two forces. One is a forward force of 1,140 newtons provided by traction between the wheels and the road. The other is a 950-newton friction force acting in the opposite direction. What is the net force used to calculate work done on the car?
______________________________________
What is the direction of this force?
______________________________________
4. Three friend help push a dead car, starting at rest on a horizontal surface. If they push the car with a constant net force of 1,200 newtons, how far must they push the car so that its final kinetic energy is 4,200 joules?
(Disregard friction.)
• 3.5 m
• 8.3 m
• 3,000 m
• 5,400 m

1. is not completed because your force did not move the wall.
2. Each truck should be timed carrying the same load for the same distance.
3. 190 N, forward
4. 3.5 m

Reference:

Complete Test Preparation for the GED Test 2014 by Steck-Vaughn