Phys Sci Chapter 3

Work

product of the applied force and the parallel distance through which the force acts

work formula

work = force x distance

2 important facts of work

something must move whenever work is done and the movement must be in the same direction of the force

in the metric system the unit of work is

joule

1 joule =

1 newton-meter

in the English system the most common unit of work is

ft-lb

power

rater at which energy is transformed or the rate at which work is done

power formula

power= work/time

the unit for power is

watts

1 watt =

1 joule/second

potential energy

energy due to position or amount of work required to lift an object to a height

Potential energy formula

gravitational potential energy (GPE) = weight x height

Kinetic energy

the energy of motion

kinetic energy can be measured in terms of

the work done to put the object in motion

kinetic energy formula

kinetic energy = ½ (mass)(velocity)²

Law of Conservation of Energy states

Energy is never created or destroyed

energy can be categorized into five forms:

mechanical, chemical, radiant, electrical, and nuclear

fossil fuels

contain the stored radiant energy of organisms that lived long ago

some renewable energy sources include:

solar cells, wind energy, biomass, and geothermal

A force of 200 N is needed to push a table across a level classroom floor for a distance of 3 m. How much of the work was done on the table?

600 j

How much work is done in raising a 10.0 kg backpack from the floor to a shelf 1.5 m above the floor?

147 j

If 5000 j of work is used to raise a 102 kg crate to a shelf in a warehouse, how high was the crate raised?

5 m

A 60.0 kg student runs up a 5.00 m high stairway in a time of 3.92 s. How many watts of power did she develop?

750 W

What is the kinetic energy of a car moving at 72 km/h?

400,000 j

How much work is needed to stop a 1000.0 kg car that is moving straight down the highway at 54.0 km/h?

112,500 j

A 1000 kg car stops on top of a 51.02 m hill. How much energy was used in climbing the hill? How much potential energy does the car have?

499,996 j (energy to climb hill AND potential energy

A horizontal force of 10.0 lb is needed to push a bookcase 5 ft across the floor. How much work was done on the bookcase? How much did the gravitational potential energy change as a result? (HINT: It’s okay to use ft-lb as the unit; no conversion to metric is necessary.)

50 ft lb, No GPE as there was no change in height

How much work is done in moving a 2.0 kg book to a shelf 2.00 m high? What is the change in potential energy of the book as a result? How much kinetic energy will the book have the instant before it hits the ground?

Change in PE: 39.2 j

KE 39.2 j

170.0 lb student runs up a stairway to a classroom 25.0 ft above ground level in 10.0 s. How much work did the student do? (kg = 2.205 lb; 1 m = 3.281 ft)

Mass of student: 77kg

Distance above ground in m: 7.62m

W=5750 j