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lecture20[1]

# lecture20[1] - Work and Kinetic Energy Kinetic Energy and...

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1 Physics 1D03 Work and Kinetic Energy Kinetic Energy and the Work-Energy Theorem Serway 7.4, 7.5 Suggested Problems : Chapter 7, problems 27, 31, 33, 39 Physics 1D03 Varying force: Work is the area under a graph of force vs. distance (include only the force component parallel to the motion) dx F W x x f i = i x f x F x (x) x

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2 Physics 1D03 Example: an ideal spring. Hooke’s Law: The tension in a spring is proportional to the distance stretched. or, | F | = k | s | The spring constant k has units of N/m Directions: The force exerted by the spring when it is stretched in the + x direction is opposite the direction of the stretch: F = -kx Work by forces which are not constant Physics 1D03 i x f x Work by a Spring F s F s = - kx Find a function W(x) so that dx dW x F s = ) ( W = ½ k ( x i 2 x f 2 ) or , W = area under curve: x i x f F s x
3 Physics 1D03 Quiz A physicist uses a spring cannon to shoot a ball at at a stuffed gorilla. The cannon is loaded by compressing the spring 20 cm.

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