9. Work & Energy

Intro to Calculating Work

9. Work & Energy

# Intro to Calculating Work - Video Tutorials & Practice Problems

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concept

## Work Done by a Constant Force

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2

Problem

ProblemYou pull a 5kg box vertically up with a constant 100N force for 2m. How much work do you do?

A

51 J

B

100 J

C

102 J

D

200 J

E

500 J

F

1000 J

3

example

## Work by a 2D Push/Pull

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4

example

## Work Done By Friction

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5

concept

## Work Done By Gravity

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6

Problem

ProblemYou push a 3kg box against a wall for a distance of 2m with a force of 40N that makes a 53° angle with the horizontal, as shown. Calculate the work done by gravity.

A

58.8 J

B

-58.8 J

C

- 160 J

D

-80 J

7

example

## Work Done on Curvy (Not straight) Paths

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PRACTICE PROBLEMS AND ACTIVITIES (26)

- A factory worker pushes a 30.0-kg crate a distance of 4.5 m along a level floor at constant velocity by pushin...
- Two tugboats pull a disabled supertanker. Each tug exerts a constant force of 1.80×106N, one 14° west of north...
- A factory worker pushes a 30.0-kg crate a distance of 4.5 m along a level floor at constant velocity by pushin...
- A factory worker pushes a 30.0-kg crate a distance of 4.5 m along a level floor at constant velocity by pushin...
- (I) A 55.0-kg firefighter climbs a flight of stairs 28.0 m high at constant speed. How much work does she do?
- (II) Estimate the work you do to mow a lawn 10 m by 20 m with a 50-cm-wide mower. Assume you push with a horiz...
- A 25 kg air compressor is dragged up a rough incline from r₁ (→ above r)= (1.3î + 1.3ĵ) m to r₂ (→ above r) = ...
- The energy used to pump liquids and gases through pipes is a significant fraction of the total energy consumpt...
- A 1000 kg elevator accelerates upward at 1.0 m/s² for 10 m, starting from rest. (b) How much work does the ten...
- The three ropes shown in the bird's-eye view of FIGURE EX9.18 are used to drag a crate 3.0 m across the floor....
- Objects that rotate in air or water experience a torque due to drag. With quadratic drag, a drag torque that's...
- Consider a force F(𝓍) = A𝓍³⸍² acting on an object moving in a straight line. Assume that A = 10.0 N/mᶻ. (b)...
- (II) In a certain library the first shelf is 15.0 cm off the ground, and the remaining four shelves are each s...
- (II) A lever such as that shown in Fig. 7–20 can be used to lift objects we might not otherwise be able to lif...
- (I) The head of a hammer with a mass of 1.2 kg is allowed to fall onto a nail from a height of 0.65 m. What is...
- (III) A 2800-kg space vehicle, initially at rest, falls vertically from a height of 2900 km above the Earth’s ...
- A package of mass m is placed onto a horizontal conveyor belt moving at speed v (Fig. 7–32). The coefficient o...
- A softball having a mass of 0.25 kg is pitched horizontally at 120 km/h. By the time it reaches the plate, it ...
- (II) A constant force F→ = (2.0 î + 4.0 ĵ) N acts on an object as it moves along a straight-line path. If the ...
- (II) A child is pulling a wagon down the sidewalk. For 5.0 m the wagon stays on the sidewalk and the child pul...
- An airplane pilot fell 370 m after jumping from an aircraft without his parachute opening. He landed in a snow...
- (II) Consider a force F₁ = A /√x which acts on an object during its journey along the x axis from x = 0.0 to x...
- (III) A 3.0-m-long steel chain is stretched out along the top level of a horizontal scaffold at a construction...
- Two forces, F₁→ = (1.50î - 0.80 ĵ + 0.70k̂) N and F₂→ = ( - 0.70î + 1.20 ĵ) N, are applied on a moving object ...