The maximum speed of a mass m on an oscillating spring is vmax . what is the speed of the mass at the instant when the kinetic and potential energy are equal?

Respuesta :

Let
A =  the amplitude of vibration
k =  the spring constant
m =  the mass of the object

The displacement at time, t, is of the form
x(t) = A cos(ωt)
where
ω =  the circular frequency.

The velocity is
v(t) = -ωA sin(ωt)

The maximum velocity occurs when the sin function is either 1 or -1.
Therefore
[tex]v_{max} = \omega A[/tex]
Therefore
[tex]v(t) = -V_{max} sin(\omega t)[/tex]

The KE (kinetic energy) is given by
[tex]KE = \frac{m}{2}v^{2} = \frac{m}{2} V_{max}^{2} sin^{2} (\omega t)[/tex]

The PE (potential energy) is given by
[tex]PE = \frac{k}{2} x^{2} = \frac{k}{2} A^{2} cos^{2} (\omega t)[/tex]

When the KE and PE are equal, then
[tex]v^{2} = \frac{k}{m} A^{2} cos^{2} (\omega t)[/tex]

For the oscillating spring,
[tex]\omega ^{2} = \frac{k}{m} \\ V_{max} = \omega A = \sqrt{ \frac{k}{m} } A [/tex]
Therefore
[tex]v^{2} = \frac{k}{m} \frac{m}{k} V_{max}^{2} cos^{2} ( \sqrt{ \frac{k}{m} t} ) \\ v = V_{max} \,cos( \sqrt{ \frac{k}{m} t} )[/tex]

Answer: [tex]v(t) = V_{max} cos( \sqrt{ \frac{k}{m} t} )[/tex]