phy

The problem statement: On October 15, 1997, driver Andy Green drove a vehicle dubbed the ThrustSuperSonicCar (ThrustSSC) faster than the speed of sound, officially breaking the sound speed barrier in a land vehicle. The course he drove is 13 miles long. The first 6 miles are used to get the car up to speed. The next mile is timed, and Green’s speed over the timed mile broke the record. The last 6 miles are used to slow the car back down. According to the rules, Green had to make two runs within 1 hour. His speed averaged over the two runs of the timed mile was reported as 763.035 mph (1233.704 km/h).

Assume the acceleration was constant over the first and last 6 miles and the velocity was constant over the timed mile. Report your answers to a conservative three significant figures (rather than seven!). First, find the acceleration for the first 6 miles, and then find the time taken at top speed to set the record.

The problem steps and strategy:

Interpret and Anticipate

Represent the given information in context in the simple sketch. Notice how the sketch helps us identify three distinct parts to the motion of the ThrustSSC. Include an appropriate coordinate system.

Solve

Convert numerical information to standard SI units (these are included on the sketch).

List known and unknown variables, and those that are not needed. (Some of these steps are intended to be done on a whiteboard or other classroom presentation, or by students in class.)

Choose equations for each part to fit the need of the problem and incorporate the known information.

Do algebra first.

Insert numerical values and express the answer. [acceleration is 6.08 m/s2 in the +x direction; time for the mile is 4.70 s]

Check and Think

Compare to some known values, such as the time it takes a car on the highway to travel one mile, roughly 60 seconds.

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