work. work …is a force acting through a distance. work is only done, when a force moves an object...

WorkWork

Work…is a force acting through a

distance.Work is only done, when a force moves

an objectAnd the object must be moved in the

direction of the force

In other words... Work = Force x distance (W = Fd)

d

Work cont.Is work done in the following examples...

1.You push as hard as you can against a door, but it does not move.No: there is no movement

2.You lift a basketball off the floor.Yes: there is force and distance

3.Superman stops a speeding jet.No: there is not movement in the direction of the

force

4.You put your backpack on and carry it to the door.No: the movement is not in the direction of the force

5.You hold your backpack for five minutes.No: there is no time involved in work

Work cont.Work is measured

in newton-meters (Nm)

-the newton is from force

-the meter is from distance

1 Nm = 1 Joule (J)

Power…is the rate at which work is done.

Power = Work TimeThe unit of power is the watt (W)1 Watt = 1 joule per second (J/s)

Electricity is measured in kilowatts (kW)

Horsepower (hp)One hp equals 750 watts

Practice Problems for

Work & Power

A car runs out of gas. Fortunately, there is a gas station nearby. You must exert force of 715 N on the car in order to move it. By the time you reach the station, you have done 2.72 x 104 J of work. How far have you pushed the car?

W= F=d=

What Formula do you need to use? _____________________

Solve the Problem:

The world’s most powerful tugboats, which are built in Finland, are capable of providing 8.17 x 106 W of power. How much work does one of these tugboats do in 12.0 s?

W=P=d=

What Formula do you need to use? _____________________

Solve the Problem: