Q1. Assume that a horse pulls a sleigh in a way that the sleigh moves at constant velocity. What is the work being done on the sleigh (a) by the horse, (b) by the Earth, and (c) by the force of friction? Determine whether the work is positive, zero, or negative.
To determine the work being done on the sleigh by different forces, we need to understand the work-energy principle. According to this principle, work is done when a force acts upon an object and causes it to move.
(a) Work done by the horse on the sleigh:
Since the sleigh is moving at a constant velocity, there is no change in kinetic energy, and therefore no net work is being done on the sleigh by the horse. This is because work is defined as the product of the force applied and the displacement of the object in the direction of the force. If the velocity is constant, the displacement is zero, resulting in zero work. So, the work done by the horse on the sleigh is zero.
(b) Work done by the Earth on the sleigh:
The work-energy principle applies only to the net work done on an object, so we need to consider all the forces acting on the sleigh. In this case, there are two forces involved: the force applied by the horse and the gravitational force exerted by the Earth. Since the velocity is constant, the net work done on the sleigh must be zero. Therefore, the work done by the Earth on the sleigh must be equal and opposite to the work done by the horse, i.e., also zero.
(c) Work done by the force of friction:
The force of friction acts opposite to the direction of motion of the sleigh, which is provided by the pulling force of the horse. The work done by friction can be determined by considering the equation W = Fd, where W represents work, F is the force, and d is the displacement. In this case, since the displacement is zero (due to constant velocity), the work done by the force of friction is also zero.
In summary:
(a) Work done by the horse on the sleigh: Zero (0)
(b) Work done by the Earth on the sleigh: Zero (0)
(c) Work done by the force of friction: Zero (0)
All the works are zero because the velocity of the sleigh is constant and there is no change in kinetic energy.