Question

A particle that hangs from a spring oscillates with an angular frequency ω. The spring-particle system is suspended from the ceiling of an elevator car and hangs motionless (relative to the elevator car) as the car descends at a constant speed v. The car then stops suddenly. (Use omega for ω, v, and t as appropriate in the following.)

a) how do we know in this case that we are using v(max)=wA instead of v.

b)x=-Asinwt, I'm confused why cant we use cos instead of sin