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Summary12

# Summary12 - Summary Lecture 12 Energy Work Force Energy is...

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Energy Ù Work Ù Force Summary Lecture 12 Energy Work Energy is the capability to do Work or To do some work you need to transform some energy. Definition of Work Work = Force x Displacement (Force component along path!) W = F s cos θ W F = F s cos Total work on object W = F Net s cos θ Energy and Work are measured in 1 Nm = 1 J [Joule] Total work done by the net force is equal to the change in kinetic energy Work – Energy Theorem to the change in kinetic energy. W = Δ KE

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Raising a Crate Bob raises a 50-kg crate by 2.0 m while Bob raises a 50 kg crate by 2.0 m while increasing the crates velocity from 1.0 m/s to 3.0 m/s. How much work is done on the crate? W = F net h cos Θ (F F ) h = 2 m net = F Bob – mg) Work Energy Theorem W = Δ KE F Bob W = ½ m v f 2 – ½ mv i 2 = 100 J mg How much work does Bob do? F Bob (Tension is non conservative) W = W C + W NC = W gravity + W Bob = -mgh + F Bob h W Bob = W + mgh = Δ KE + mgh = 1080 J
Kinetic Energy KE = m/2 v 2 In Physics 111 we study Mechanical Energies Potential Energy (Gravity) Δ PE = mgh (Spring) PE = k/2 x 2 So for the crate example we can write

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