Conservation of Energy (Spring + Kinetic)

[IB]

Tonight I've got so many hard problems...

A 3.0 kg mass slides across a frictionless surface and collides against a spring bumper with a velocity of 3.0 m/s as shown in the diagram. Determine the maximum amount of the spring compresses if it spring constant is 335 N/m.

For this one I don't know whether I should use E_kin = E_spring then solve from there or E_kin(i) + E_spring(i) = E_kin(f) + E_spring(f), but as for the former I got:

1/2 mv^2 = 1/2 k (delta) l^2
mv^2 = k(delta) l^2
(3)(3)^2 = (335) (l^2)
x = .081 m

Is that right? Thanks a lot for your help so far, everyone! I really appreciate your time and kindness.

 

[andrewchang]

looks good.

except the spring epe is .5kx^2

 

[dx]

Both the equations are valid. The second one reduces to the first one since E_spring(i) is zero and E_kin(f) is zero.