SOL2-2011

# SOL2-2011 - ECH 152A Fall 2011 Roland Faller Solution for...

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Solution for Homework 2, October 3, 2011 Problem 1. (5 points) An egg which is initially at rest is dropped on a hard surface and breaks. We wait that any temperature change equilibrates. Take the egg as system. (a) What is the sign of W ? (b) What is the sign of Δ E pot ? (c) What is Δ E kin (just before and just after impact)? (d) What is Δ U tot ? (e) What is the sign of Q ? Solution (a) W = 0 as overall no work is performed. (Gravity performs ﬁrst acceleration work on the system W > 0 and then the system performs deformation work on the ground W < 0.) (b) Δ E pot = mg Δ z < 0 as the egg looses height (c) Before Impact: Δ E kin = - mg Δ z After Impact Δ E kin = 0 (d) Δ U tot = 0 as the overall temperature and pressure do not change (state functions). (e) Q < 0 as the egg gives up its potential energy at impact Problem 2. (4 points) Complete the table for a four step cycle of a closed system. Step

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SOL2-2011 - ECH 152A Fall 2011 Roland Faller Solution for...

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