Force needed for simple harmonic motion with amplitude 15 cm

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[SOLVED] Simple Harmonic Motion question

Homework Statement


A 0.27 kg block oscillates back and forth along a straight line on a frictionless horizontal surface. Its displacement from the origin is given by the following equation.
x = (15 cm)cos[(5 rad/s)t + /2 rad)]
(a) What is the oscillation frequency? .796 Hz
(b) What is the maximum speed acquired by the block? 75cm/s
At what value of x does this occur? 0cm
(c) What is the magnitude of the maximum acceleration of the block? 375cm/s^2
At what values of x does this occur? (Type your answers in any order. If there is only one answer, type 'none' in the second box.) -15cm 15cm
d) What force, applied to the block, results in the given oscillation?

Homework Equations


x(t)=Xm Cos(wt+phi)
F=-kx

The Attempt at a Solution


I solved parts athrough c but I was not sure what to do for part d.
I had already solved for k in part a so I substituted the values for k and Xm into the F=-kx equation
F=-6.75(N/m) .15m=1.0125N
the form webassign wants the answer in is (_____ N/cm)x
 

Discussion

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# Hi
# I think there may be a mistake in the question. The dimensionality of the force is N not N/cm.
 
notice that the answer is in the form of (-----N/cm)x. the question is asking for the force F=-kx so would the answer be k with units of N/cm instead of N/m?
 
# Oh, yes. I did not see x there. Then, I think your reasoning seems plausible. You should write -k in units of N/cm there.