Question involving conservation law and springs

[mizzy]

i'm sorry...the speed should be 4.2m/s because that is the speed right after collision.

I get a k of 7962.5N/m and therefore T = 3.60s

Can you confirm this?

THANKS FOR ALL YOUR HELP! =)

 

[kuruman]

Confirmed. Don't forget that 3.60 s is not the time you are looking for.