244_Dynamics 11ed Manual

# 244_Dynamics 11ed Manual - W has a velocity v A when it is...

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Engineering Mechanics - Dynamics Chapter 14 Problem 14-1 A woman having a mass M stands in an elevator which has a downward acceleration a starting from rest. Determine the work done by her weight and the work of the normal force which the floor exerts on her when the elevator descends a distance s . Explain why the work of these forces is different. Units Used: kJ 10 3 J = Given: M 70 kg = g 9.81 m s 2 = a 4 m s 2 = s 6m = Solution: Mg N p Ma = N p Mg Ma = N p 406.7 N = U W Mgs = U W 4.12 kJ = U NP s N p = U NP 2.44 kJ = The difference accounts for a change in kinetic energy. Problem 14-2 The crate of weight
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Unformatted text preview: W has a velocity v A when it is at A . Determine its velocity after it slides down the plane to s = s' . The coefficient of kinetic friction between the crate and the plane is μ k . Given: W 20 lb = a 3 = b 4 = v A 12 ft s = s' 6 ft = k 0.2 = Solution: θ atan a b ⎛ ⎝ ⎞ ⎠ = N C W cos ( ) = F k N C = Guess v' 1 m s = Given 1 2 W g ⎛ ⎝ ⎞ ⎠ v A 2 W sin ( ) s' + F s' − 1 2 W g ⎛ ⎝ ⎞ ⎠ v' 2 = v' Find v' ( ) = v' 17.72 ft s = 242...
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