3 Sam attaches a 0.5 kg weight to a spring with spring constant k = 80 N/m and l

Question

3 Sam attaches a 0.5 kg weight to a spring with spring constant k = 80 N/m and lets it settle to its equilibrium point. She then pulls the weight down a distance d (as we did in the lab this week) by doing 40 J of work on the weight. Sam then releases the weight. How much kinetic energy does the weight have when it returns to its equilibrium position? a) Less then 40 J b) Exactly 40 J c) More than 40 J d) None of the above 4. Suppose you pull a box (with mass m) friction between the box and floor with coefficient of kinetic friction . If you pull at an al horizontal, which equation accurately describes the acceleration of the box? acorss a floor with force F (as in the picture above). There is gle above the

Explanation / Answer

3.

Here,

Work done = spring energy = (1/2)kx^2

W = 40 J

Kinetic energy = (1/2)mv^2

From conservation of energy,

(1/2)kx^2 = (1/2)mv^2

so, KE = 40 J

Kinetic energy is exactly 40 J. Option (b) is correct.

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