Question

Since 1967, Tractor Pull competitors from around the country have met at the Wood County Fairgrounds

tractor's chain that is pulling Sled 5. What are the four forces acting on the sled when the tractor is pulling?

in Bowling Green, Ohio, for the National Tractor Pulling Championship (www.pulltown.com). The tractor

or truck attempts to pull a heavy weight (called the

“sled”) as far as possible, up to the length of the track

(320 feet).

You are part of the first ever Penn State Tractor Pull team, which will be competing in the

National Tractor Pulling Championship. As a physics student, the rest of your team has asked y

ou to do

some analysis to help them

optimize the angle at which to pull the sled using the tractor

.

You recognize that a tractor pull is a complex problem involving the weight distribution on the sled, the

angle at which the sled chains are attached to the tractor, the weight distribution of the tractor, the

power the tractor can generate, and the condit

ion of the track. “Let’s start off,” you tell your team, “with

a simplified version of the tractor pull where the tractor can exert a constant pulling force, independent

of the angle. That way we can concentrate our attention on just the sled. In addition,

let’s treat the sled

as a point and not worry about the weight distribution on the sled itself.”

MODEL:

•

The sled is a point mass (mass

m

) sliding on a horizontal surface (the ground) pulled by a chain,

which makes an angle

휃

above the horizontal.

•

Also, you will assume that you are not pulling hard enough to lift the very heavy sled off the

ground.

•

Neglect any forces coming from the air.

VISUALIZE

Below is a pictorial representation of the problem.

Answer 1

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