1) Points A and B are between the plates of an ideal parallel plate capacitor, s

Question

1) Points A and B are between the plates of an ideal parallel plate capacitor, separated by 10 cm. The potential at A is 4 V and the potential at B is 9 V. If the energy density at A is 3 J/m3 , then the energy density at B is:

2)  A uniform cylinder with resistance R is cut in thirds and the pieces are then attached as shown. What is the equivalent resistance?

3) An ideal horizontal spring-mass system has an amplitude of 0.4 m, spring constant k = 200 N/m and a mass of 0.5 kg. What is the speed of the mass when it is 0.2 m from the equilibrium position?

Explanation / Answer

3)

A = amplitude = 0.4 m

x = displacement = 0.2 m

m = mass = 0.5 kg

k = spring constant = 200 N/m

v = speed

using conservation of energy

maximum spring energy = spring energy at x = 0.2 + KE

(0.5) k A2 = (0.5) k x2 + (0.5) m v2

(200) (0.4)2 = (200) (0.2)2 + (0.5) v2

v = 6.93 m/s

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