# Homework Help: Oscillations and Waves

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1. Dec 3, 2015

### CMATT

A suspension bridge oscillates with an effective force constant of N/m.

(a) How much energy is needed to make it oscillate with an amplitude of 0.106 m?

(b) If soldiers march across the bridge with a cadence equal to the bridge's natural frequency and impart J of energy each second, how many minutes does it take for the bridge's oscillations to go from 0.106 m to 0.530 m amplitude, assuming the bridge has no damping?

RELEVANT EQUATIONS:
For (a)
Etot = (.05)(k)(xmax)^2

For (b)
not sure

THE ATTEMPT AT THE SOLUTION:

a)
k = 1.120E8 N/m
xmax^2 = .106 m

Etot = (.05)(k)(xmax)^2 = (.05)(1.120E8)(.106) = 6.29E5 J
This answer was correct on my webassign

b) I'm very confused here. All I know is 6.29E5 J is the energy required to make it oscillate with an amplitude of .106 m

Last edited by a moderator: Apr 17, 2017
2. Dec 4, 2015

### ehild

What is the energy when the bridge oscillates with 0.530 m amplitude?
The soldiers impart J of energy each second to the bridge. How long time is needed that the bridge get the new energy?

Last edited by a moderator: Apr 17, 2017