![]() We will prove that for a mass attached to a spring of spring constant k that has been stretched (or compressed) a distance x from equilibrium the elastic potential energy of the system is This location is called the datum or reference location for gravitational potential energy. In this we have assigned the value zero to the potential energy when the mass is at h=0. We will prove that a mass m at a vertical height above the ground h has for the mass-earth system a gravitational potential energy The reason for the minus sign will become evident later.Ĭomment: Only the change in potential matters because the work always refers to a change in position and not just one position. Mathematically, we stipulate that the work serves to increase the potential (stored) energy and write In short, potential energy is position energy. Potential energy is the energy stored in a system due to the position of the parts of the system. This stored energy is called potential energy. However, another possibility is the work simply stores the energy in the system without any change in kinetic energy. We have seen that when a force does work on a system the system acquires motion energy, i.e. NOTE: THIS LECTURE IS ONE OF THE MOST IMPORTANT THIS SEMESTER!!!! The net force acting on the skier in her direction of motion is on the box is 445.2 N.Potential energy and conservation of energy If we define the positive direction as down the hill, which is the skier's direction of motion, the net force is: The two forces to consider are the force directed down the hill and the force of kinetic friction directed up the hill. The net force acting on the skier is the sum of forces. The force that moves the skier down the hill is the remaining component of the force of gravity, F θ = mg sinθ. The force of kinetic friction opposes the motion of the skier. Using this, the formula can be used to find the magnitude of the force of kinetic friction:į k = (0.0800)(55.00 kg)(9.80 m/s 2)cos(60°) The normal force is η = mg cosθ, and the remaining force component is F = mg sinθ. The normal force is the component that is perpendicular to the angled surface, and the remaining force is parallel to the angled surface. ![]() On a surface that is at an angle relative to the horizontal axis, The total force due to gravity, F = mg, must be broken in to components. What is the magnitude of the force of kinetic friction, and what is the net force along the skier's direction of motion?Īnswer: On a flat surface, the normal force on an object is η = mg. The hill is at a 60.0° angle from the horizontal. The coefficient of kinetic friction between the skis and the snow is μ k = 0.0800. The net force acting on the box is 17.8 N forward.Ģ) A woman is skiing straight down a snow-covered hill. If we define "forward" as the positive direction, the net force is: The two forces to consider are the force of kinetic friction acting in the opposite direction as the box's motion, and the force exerted by the worker, which is 400 N forward. The net force acting on the box is the sum of forces. The force of kinetic friction acting in the opposite direction as the motion of the box is 382.2 N. Using this, the formula can be used to find the force of friction: What is the magnitude of the force of friction, and what is the net force moving the box?Īnswer: On a flat surface, the normal force on an object is η = mg. ![]() The box has a mass of 75.0 kg, and the worker is exerting a force of 400.0 Nforward. The coefficient of kinetic friction is μ k = 0.520. 1) A worker in a stock room pushes a large cardboard box across the floor.
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