
#1
Sep208, 05:19 AM

P: 15

Q: A ball is at rest on an inclined plane. It begins to roll down with an acceleration of 2 m/s^2. How long does it take the ball to roll 50 m?
This is my work: find time using, s = ut + 1/2 a t^2 t = sqrt(2s/a) Plug in the s = 50 and a = 2 Am I right? Thanks a lot. 



#2
Sep208, 05:38 AM

Math
Emeritus
Sci Advisor
Thanks
PF Gold
P: 38,881

Where have you used the fact that this is a rolling ball and not a falling mass point? In particular, you have not taken into account the rotational kinetic energy.




#3
Sep208, 09:42 AM

P: 15

Thanks for your reply.
A falling object accelerates with acceleration of gravity, g. Here the given acceleration, as I understand, is the acceleration of the center of mass (linear acceleration). Even though the ball is rolling, C.M is moving in a straight line along the incline so that we can use the equation of kinematics. 



#4
Sep208, 11:38 AM

HW Helper
P: 5,346

rolling ballX = 1/2 a t^{2} in this case because you are given its constant acceleration. 


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