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Re: [Phys-l] crutches versus shoes

At 9:15 PM -0400 4/18/11, Anthony Lapinski wrote:
Do we want our students to solve a problem like this?:

A train traveling from New York to Chicago is moving at 110 km/h when the
engineer sees a stalled car near the track ahead. The train brakes to a
halt in 1.2 min with a constant deceleration, stopping just next to the
car. How far was the train from the car when the engineer first applied
the brakes?


My students would read the problem and say:

OK, I need to find the area under the velocity-time graph that I have just sketched here on my paper.
The base is 1.2 minutes and the height is 110 km/hr.
The area is 1/2 (1.2 minutes) x ( 110 km/hr) = 66 km minutes / hour.

Then they would clean up the units - having already shown the physics involved.


(Well, I remember a FEW who would have done it that way ;-) )