Download Work and Power Problems

Work and Power Problems
Use this PowerPoint to learn how to solve work and power problems.
This is for the handout with only 6 questions.
Work
• Work = Force multiplied by Distance
• 𝑊 =𝐹×𝑑
• For work to be done, a force must be applied to an object and the
object must move in the direction of the force
• If the object remains stationary (doesn’t move) then no work has
been done.
• The unit for Work is Joules (J)
Problem 1:
Renatta Gass is out with her friends. Misfortune occurs and
Renatta and her friends find themselves getting a workout. They
apply a cumulative force of 1080 N to push the car 218 m to the
nearest fuel station. Determine the work done on the car.
W=Fxd
W = 1080 N x 218 m
W = 235440 J
Problem 2:
Hans Full is pulling on a rope to drag his backpack to school across the
ice. He pulls with a force of 22.9 Newtons to drag his backpack a
horizontal distance of 129 meters. Determine the work (in Joules) done
upon the backpack.
• This problem is just like Problem 1.
• The correct answer is: 2954.1 J
• Now go to the next slide and try number 4, yes I know I skipped
number 3. Don’t worry, we’re going to go back.
Problem 4:
Sheila has just arrived at the airport and is dragging her suitcase
to the luggage check-in desk. She pulls on the strap with a force
of 190 N to displace the suitcase 45 m to the desk. Determine
the work done by Sheila on the suitcase.
• This problem is just like Problem 1.
• The correct answer is: 8550 J
• Now let’s go back and look at number 3.
Problem 3:
Lamar Gant, U.S. powerlifting star, became the first man to deadlift five
times his own body weight in 1985. Deadlifting involves raising a loaded
barbell from the floor to a position above the head with outstretched
arms. Determine the work done by Lamar in deadlifting 300 kg to a
height of 0.90 m above the ground. (Force = mass * 9.8)
• Notice that you don’t have a force, only a mass
• Use the force formula above to calculate the force:
• F = m * 9.8
• F = 300 kg * 9.8
• F = 2940 N
This is not the answer, just the force that you need calculate the work.
Continued on the next slide.
Problem 3:
Lamar Gant, U.S. powerlifting star, became the first man to deadlift five
times his own body weight in 1985. Deadlifting involves raising a loaded
barbell from the floor to a position above the head with outstretched
arms. Determine the work done by Lamar in deadlifting 300 kg to a
height of 0.90 m above the ground. (Force = mass * 9.8)
• W=F*d
• W = 2940 * 0.90
• W = 2646 J
• Now you try Problem 6a
Problem 6:
During the Powerhouse lab, Jerome runs up the stairs,
elevating his 102 kg body a vertical distance of 2.29
meters in a time of 1.32 seconds at a constant speed.
a. Determine the work done by Jerome in climbing the
stair case.
• This problem is just like Problem 3. (ignore the time)
• The correct answer is: 2289 J
Power
• Power = Work divided by time
• 𝑃 =𝑊÷𝑡
• Power is directly related to work, so if the work increases then the
power will also increase.
• Power is indirectly related to time, so if the time increases then the
power will decrease.
• The unit for Power is Watts (W)
A lawnmower does 300 Joules of work in 3
minutes. How much power does the mower
have?
• 𝑃 =𝑊÷𝑡
• Time must be in seconds so… 3 minutes = 180 seconds
• 𝑃 = 300 𝐽 ÷ 180 𝑠
• 𝑃 = 1.67 𝑊
Now it’s your turn to work…
• Complete the handout titled: Work and Power Practice Problems.
• You should complete questions 1 – 10.
• Number 9 is more difficult than the other problems, but I think you
can do it. Remember that 1 kilometer = 1000 meters.
• Turn in both handouts at the end of class.
• Have a great weekend.