Work and Energy - Mission WE2 Detailed Help

In a physics lab, a 60-kg student runs up a 2-meter tall flight of stairs in 1.5 seconds. The student's power rating is approximately _____ W.

Work (W) is calculated from knowledge of the force (F) that acts upon an object, the displacement (d), and the angle (Θ) between the F and d vectors. The formula is
W = F • d • cosine(Θ).

Power (P) is calculated from knowledge of the work done upon an object (W) and the time (t) required to do this work. The formula is

P = W / t

Timing the task of running up a flight of stairs is a common method of determining a student's power rating. On each step, there is an upward force that is exerted upward on the student to lift him a vertical distance. With a good head of steam heading into the stair case, the horizontal motion is maintained by the student without any significant need to sustain it with a forward force. The vertical force is equal to the weight of the student (see Formula Frenzy section) if a constant vertical motion is assumed. Since the mass is given, this vertical force can be determined.

Calculating the power demands that the work done by the student is first calculated. Once calculated, it is divided by time to determine the power. The equations are provided in the Formula Frenzy section. It is a two-step calculation with very little tricks involved other than the trick of determining the force from the mass of the student (as discussed in previous paragraph).


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