when is velocity negative in Simple harmonic motion?

Question

Imagine this spring block system resting horizontally, it oscillates left and right... when is the velocity negative? Is it when it the block travels from the right max displacement to the equilibrium point

OR

when it travels from right max displacement to left max displacement? Im confused when trying to find the phase angle in the unit circle...

for instance the problem says the block has mass 0.2kg   with k= 5N/m and at time π/10s it compresses by 6cm and has velocity of -40cm/s...  how do i choose the correct phase angle

denis · Answer

Amy :

I understand that, but the problem I explained above has a phase angle solution of -2.5rad, or 2π - 2.5 rad  which means its in the 3rd quadrant of the unit circle, but that means the velocity is positive since if the motion is on the circle and projected on the x axis, the object appears to move right but it says it has a negative velocity?

Amy · Answer

The sign of velocity indicates the direction of motion.
If you've defined right=positive, then all right-to-left motion has negative velocity.

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when is velocity negative in Simple harmonic motion?

2 Answers