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NOTES 16 - Topic 2 - Mechanics ;

NOTES 16 - Topic 2 - Mechanics ; ------------------------------------------------------------------------------------------------- 2 .3.1 Define Work • WORK - an unbalanced force causes an object to move; a scalar quantity;

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NOTES 16 - Topic 2 - Mechanics ;

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  1. NOTES 16 - Topic 2 - Mechanics; ------------------------------------------------------------------------------------------------- 2.3.1 Define Work • WORK - an unbalanced force causes an object to move; a scalar quantity; • When work is done on an object, it’s energy changes by the amount of work done (Work-Energy Principle). • Work is defined as the product of the distance an object moves and the net force acting on the object in a direction parallel to the direction of movement. Work = forceparallel• distance; W = F • d cos θ Work = (kg•ms-2) • m = kg•m2s-2 =N•m = Joules (J)

  2. 2.3.2Determine the work done by a non-constant force by interpreting a force-displacement graph

  3. 2.3.3 Solve problems involving the work done on a body by a force; Sample Problem 7: A 20.0 kg box requires a 150. N horizontal force to move it a distance of 10.0 m. (A) How much work is done? (A) How much work would be required to raise it the same distance vertically? (show solutions in NB) (A) Given: Unknown: Equation: (B) Given: Unknown: Equation:

  4. 2.3.4 Define kinetic energy; KINETIC ENERGY - the energy an object has because it is moving; KE = (1/2)mv2 = kg•(ms-1)2 = kg m2 s-2 = N•m = Joules Coast Guard Island Class Cutter Top Speed = 40. knots = 74 kmh-1 = 21 ms-1; Mass = 150 tonnes = 150,000 kg; KE = (1/2)mv2 =

  5. 2.3.5 Describe the concepts of gravitational potential energy and elastic potential energy POTENTIAL ENERGY - the amount of energy “stored” in a system due to its position or configuration; the ability to do work at some time in the future; a scalar quantity; • Types of Potential Energy - gravitational elastic (spring or rubber band) nuclear electrical chemical

  6. Gravitational Potential Energy - potential energy held by an object due to its height above ground level. PEg = mgh = mass x (acceleration due to gravity) x height PEg = kg•(ms-2)•m = kg•m2s-2 = Joules (J) Mass of Boulder = 100. tonnes = 100,000 kg Distance to bottom of cliff = 100. m PEg = mgh =

  7. Elastic Potential Energy - the energy stored by the compression or stretch of an elastic material; PEe = 1/2 kx2 =(Nm-1) (m2) = Nm = J where k = spring constant (Nm-1) x = stretch or compression (m) Stretch of Bungee Cord = 30.m kbungee = 100. Nm-1 PEe = 1/2 kx2 =

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