Ch 13-1-science

power

(physics) the rate of doing work

work

A form of energy that comes from force applied over distance. A force of 1 newton does 1 joule of work when the force causes 1 meter of motion in the direction of the force.

mechanical advantage

A quantity that expresses how much a machine multiplies force or distance.

Describe how a ramp can make lifting a box easy without changing the amount of work being done,

A ramp allows the use of a smaller force exerted over a longer distance, so that work is unchanged.

A bus driver applies a force of 55 N to the steering wheel, which in turn applies 132 N of force to the steering column. What is the mechanical advantage of the steering wheel?

MA = 132/55 = 2.4

An outboard engine on a boat can do 1.0 x 10^6 J of work in 50.0 s. Calculate its power in watts. Convert your answer to horsepower (1 hp = 746 W)

P = 10^6 / 50 s = 20000 W 20000W / 746 = 26.8 hp

While rowing across the lake during a race, Johndoes 3960 J of work on the oars in 60.0 s. What is power output in watts?

P = W/t = 3960 J/60.0 s = 66.0 watts

Power equation

Power= Work/Time

Both a short ramp and a long ramp reach a height of 1 m. Which ramp has a greater mechanical advantage?

The long ramp has a greater mechanical advantage than the short ramp.

How much work is done by a person who uses a horizontal force of 25 N to move a desk 3.0 m?

W = 75 J

An apple weighing 1 N falls a distance of 1 m. How much work is done on the apple by the force of gravity?

W=(1 N) (1 m) = 1J

A bicycle's brakes apply 125 N of frictional force to the wheels as the bike moves 14.0 m. How much work do the brakes do?

W=(125 N)(14.0 m) = 1.750 J

A crane uses an average force of 5000 N to lift a girder 25 m. How much work does the crane do on the girder?

W=(5200 N)(25 m) =1.3 x 10^2 J

A mechanic uses a hydraulic lift to raise a 1200 kg car 0.5 m off the ground. How much work does the lift do on the car?

Work = Force x Distance and the force is the gravitational force W = (1200 kg)(9.8 m/s^2)(0.5 m) = 5900 J

Define work and power. How are work and power related?

Work is the quantity of energy transferred by a force applied to an object that moves in the direction of the force. Power is a quantity that measures the rate at which work is done. Power equals work divided bu time.

Anna walks up the stairs on her way to class. She weighs 565 N, and the stairs go up 3.25 m vertically? If Anna climbs the stairs in 12.6 s, what is her power output? b. What is her power output if she climbs the stairs in 10.5 s?

a. P = W/t = [(565 N) (3.25 m)]/12.6 s = 140 W. b. P = [565 N](3.25 m)]/10.5 s = 175 W

A 400 N student climbs up a 3.0 m ladder in 4.0 s. a. How much work does the student do? b. What is the student's power output?

a. W = 400 x 3 = 1200 J b. P = 1200/4 = 300 W

Determine if work is being done in the following situations: a. lifting a spoonful of soup to your mouth b. holding a large stack of books motionless over your head c. letting a pencil fall to the ground.

a. yes b. no c. yes (by gravity)

mechanical advantage equation

output force/input force = input distance/output distance

What is SI unit of power?

watt (W)