# Math Help - Velocity from displacement

1. ## Velocity from displacement

Hi the question is as following,
The displacement of a body after time t is given as s = tsint + cost. Calculate its velocity and acceleration values at t = 3
(an: -2.970; -1.413)

I used equation ds/dt = v to find the derivative which is
v = tcost + sint -sint
but when i put t = 3 to the equation can't get the right answer, I thought it would be the problem of the derivation but I can't find which goes wrong.

2. Originally Posted by yanmingfu
Hi the question is as following,
The displacement of a body after time t is given as s = tsint + cost. Calculate its velocity and acceleration values at t = 3
(an: -2.970; -1.413)

I used equation ds/dt = v to find the derivative which is
v = tcost + sint -sint
but when i put t = 3 to the equation can't get the right answer, I thought it would be the problem of the derivation but I can't find which goes wrong.
Your derivative is correct so your mistake lies elsewhere.

3. oh, I just found where goes wrong, when I put t = 3 in equation I forgot to change it the the degree 3 = 171.88 degree thanks anyway.