Jim Guinn’s PHYS1111 Assignment #16 Solutions
These problems are not to be handed in.
They are for you to study for the exam.
1. A horizontal spring exerts a restoring force of 15.0N when it is displaced 5.00cm . What is
its spring constant?
From the definition of the spring constant we have
F = kx , so
k = F / x =  (15.0N) / 5.00x10
2
m =
k = 300. N/m .
Why is "F" negative, you might ask? Remember that it is a restoring force, so that it is in
the opposite direction to the displacement. Therefore, if "x" is positive, "F" must be negative.
The sign is really only important when you are thinking about the direction, so you can ignore it
if you are just thinking about the magnitudes.
2. A 7.25kg mass is connected to a horizontal spring which oscillates 5.00 times in 2.00sec .
The period of the motion is
T = (2.00s) / (5.00 oscillations) = 0.400s .
a.) What is the spring constant of the spring?
We have that
ϖ
= 2
π
/ T = 2
π
/ (0.400s) = 15.7rad/s , and
ϖ
=
√
(k / m) , so
k = m
ϖ
2
= 7.25kg * (15.7rad/s)
2
=
k = 1790 N/m .
b.) What is the maximum velocity of the mass (i.e. what is the fastest that the mass
moves during the motion) if its amplitude is 4.00cm ?
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 Spring '11
 lomant
 Force, Simple Harmonic Motion, Ω, horizontal spring

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