Question

A boy in a wheelchair (total mass 56.5 kg) has speed 1.40 m/s at the crest of a slope 2.05 m high and 12.4 m long. At the bottom of the slope his speed is 6.30 m/s. Assume air resistance and rolling resistance can be modeled as a constant friction force of 41.0 N. Find the work he did in pushing forward on his wheels during the downhill ride.

Answer 1

Answer: 439.01 J

Explanation:

The Kinetic Energy at the top + Potential Energy at the top + Work Done = Kinetic Energy at the bottom + Friction loss

1/2mv² + mgh + W = 1/2 mv² + Fd

1/2 * 56.5 * (1.4)² + 56.5 * 9.8 * 2.05 + W = 1/2 * 56.5 * (6.3)² + 41 * 12.4

1/2 * 56.5 * 1.96 + 56.5 * 9.8 * 2.05 + W = 1/2 * 56.5 * 39.69 + 41 * 12.4

55.47 + 1135.085 + W = 1121.243 + 508.4

1190.555 + W = 1629.643

W = 1629.643 - 1190.555

W = 439.088

W = 439.09 J