#### Transcript of Work and the Work Energy Theorem

**Work Theorem**

**Sample Questions**

**End**

**Work**

**FRQ**

**Work and the Work Energy Theorem**

Work

Work- requires that a force be applied and that this force be applied over some displacement

Useful Equations for Solving

Sample Question 1

Sample Question 2

A 5.6 N weight is lifted 2.2 meters. How much work is done?

Sample Question 3

A weightlifter lifts a 2000 N weight to a height of 2 m in 1 second. Another weightlifter lifts a

2000 N weight to a height of 2 m in 2 seconds.

(a) Which weightlifter did more work?

(b) Which weightlifter required more power?

An 80 kg object is to be pulled to the top of a 6.0 m ramp by a rope, the other end of

which is pulled up by a 2400 W electric winch. The ramp forms a 30° angle with the

horizontal. The coefficient of kinetic friction between the ramp and the object is 0.6 and

the coefficient of static friction is 0.8. The object moves up the ramp at a constant

velocity.

Free Response Question Solution

To Calculate Work- multiply the force applied by the displacement

Units used- Joules

Work is scalar

There are two ways of multiplying vectors:

Cross product- Gives vectors as an answer

Dot Product- Gives a scalar as an answer

Work Energy Theorem-

If work is done on an object, some of the work results in the displacement or position change of the object

1. Suppose a car with a miracle engine is able to convert into work 100% of the energy released

when gasoline burns (40 million joules per liter). If the air drag and overall frictional forces on

the car traveling at highway speed is 500 N, what is the upper limit in distance per liter of

gasoline the car could cover at highway speed?

W = Fd d = W / F = 40,000,000 J / 500 N = 80,000 m = 80 km

W = Fd = (5.6 N)(2.2 m) = 12.32 J

First lifter: W = Fd = (2000 N)(2 m) = 4000 J

Second lifter: same

A)

B)

First lifter required more power:

P = W / t = 4000 J / 1 s = 4000 watts

Second lifter: P = 4000 J / 2 s = 2000 watts

Free Response Question

A. On the diagram of the object below, draw vectors

showing all the forces on the object. Label each one.

B. Determine the maximum constant speed at which the winch can pull the object up the

ramp

C. Determine the total amount of work that the winch must do in pulling the object up the

ramp.

A)

B)

C)

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