Asked in PMC Practice Test 12 (2021) 2021Moderate

A cyclist come to skidding stop in 10 m, the force on the cycle due to the road is 200 N and opposite to the motion. how much work does the road do on the cycle:

Correct answer: B. -2000J

  • A. 2000J
  • B. -2000J
  • C. 0J
  • D. 200J

Explanation

Work is defined as the product of force and displacement in the direction of the force. In this case, the force on the cycle due to the road is opposite to the motion, so the displacement and force have opposite directions. The work done by the road on the cycle is given by the equation: Work = Force x Displacement x cos(angle) Since the force and displacement have opposite directions, the angle between them is 180 degrees, and cos(180 degrees) = -1. Therefore, the work done by the road on the cycle is: Work = 200 N x 10 m x cos(180 degrees) = -2000 J The negative sign indicates that the work done by the road is in the opposite direction of the displacement, which is consistent with the force opposing the motion of the cyclist.

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Work is done when a force produces displacement, with its value determined by the component of force along the displacement. The topic covers positive, negative and zero work, work by variable forces from force-displacement graphs, and the connection between net work and change in kinetic energy.

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