## AravindG 5 years ago how to calculate v,and a from this graph??

1. AravindG

|dw:1327254348794:dw|

2. AravindG

u see i need a and v at -1.5

3. anonymous

Put some labels on the axes :D.

4. AravindG

actually i need only sign of a and v

5. anonymous

Like gogind said, we need labels. We have no idea how "v" or "a" relates to this sine wave.

6. AravindG

|dw:1327295200296:dw|

7. AravindG

sorry for tht

8. anonymous

If that is x on the y-axis, as in distance. then you would get v(t) as at derivative of x(t) with respect to t (change in distance over time is velocity) . Similarly you would get a(t) as the derivative of v(t) with respect to t or second derivative of x(t) with respect to t (change is velocity over time is acceleration). Now you have to figure out what x(t) is. It is $\ x(t) = -sin(\pi t)$ so now: $\ v(t) = \frac{d x(t)}{dt}$$\ a(t)=\frac{dv(t)}{dt}=\frac{d^2x(t)}{dt^2}$ All you have to do now is differentiate.

9. anonymous

Actually, $\ x(t) = -Asin(\pi t)$, Where A is the amplitude of the sine wave. You didn't provide the amplitude so I assumed it's 1.

10. anonymous

|dw:1327325940478:dw| always draw a tangent to the given point at the curve here at -1.5m,tangent6 is parallel to x-axis so NO ANGLE MADE WITH X-AXIS now for acceleration,take any point b before the time (-2 seconds is less than -1.5 seconds) then draw a tangent at b we cxan see that it makes an obtuse angle with x=axis meaning -ve velocity accleration=0-(-velocity)/time=+ve acceleration edhe pole tangent varachu nooki angle nooki sum cheidhal answer kitum!

11. AravindG

thx salini i was looking for tht answr very helpful thx thx gogind too

12. AravindG

one doubt y we take v as -ve wen angle is obtuse?

13. anonymous

the basic trignometry defines tan@ of obtuse angles to be -ve(2nd quadrant)