Your equation for velocity should be: v(t) = (10 cm/s) × sin(ωt) = (0.1 m/s) × sin(ωt) or. v(t) = (10 cm/s) × cos(ωt) = (0.1 m/s) × cos(&
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Option 3 is correct. The velocity must me zero, otherwise it would keep moving and it would not really be at maximum displacement! The magnitude of the force depends on the displacement
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UPDATE: to add velocity correction. Motion will be of form y=Acoswt. w^2=k/m=25/0.5=50. w=7.071 rad/s. A=10cm. y(1)10cos(7.071*1)7.05 cm. velocity=dy/dt=Awsinwt. v(1)dy/dt(1)10*7.071
http://answers.yahoo.com/question/index?qid=201201...

The position of an object in SHM is given by [see Source 1] (1) x(t) = A * cos (ωt) and the velocity is (by differentiating) (2) v(t) = A * ω * sin (ωt) where:
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