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Work• It is defined as the product of the force applied upon an object and the distance that the object is moved in the direction of the force.
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• For work to be done, two things must occur: 1. You must apply a force to an object. 2. The object must move in the same direction as the force you apply.
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• Example1:A force of 12 Newton acts on an object over adistance of 15 meter. What is the work in Nm?
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Unit of Work• Another common unit of energy is the calorie. 1 calorie (cal) is equal to 4.18 joules (J). 1cal = 4.18 J
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Examples:• Example2:An object is pulled 4 m on a horizontal surfaceby applying a force of 50 N. Calculate the workdone on the object.• Example3:A boy pushes a box for 50 m on a frictionlesssurface and he does a work of 10000 J. Find theforce that he applies to the box.
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What is energy?• It is the ability to do work.• We do work by using energy, so we can say that work and energy should have the same units: joule (J).
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TYPES OF ENERGY• Potential Energy: It is the energy of an object due to its position.• By raising an object from the ground to a height h, we change its position, by applying a force at list equal to its weight. So we do work against the force of gravity. The work done on the object is stored as potential energy.
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Example:• A man lifts up a 4.5 kg box on to a table which is 120 cm high. How much potential energy does the box gain? (g= 10 N/kg)
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• Kinetic Energy: It is the energy of an object due to its motion.• Kinetic energy (EK) of an object of mass m moving at a speed v and is given as;
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Example:• A cyclist has a mass of 43 kg and his bicycle weighs 7 kg. If the cyclist moves with a speed of 4 m/s in the forest, what will his kinetic energy be?
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• Mechanical energy: It is the total amount of potential and kinetic energy in a system. Mechanical energy=potential energy + kinetic energy
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