Posted by Mare on Wednesday, November 18, 2009 at 11:07pm.
After the child stops pushing, the rotational acceleration is negative. it slows down.
Use the equation
alpha = L/I
where alpha is the angular DEceleration, I is the moment of inertia and L is the frictional torque.
To determine how long it takes to stop. you need to calculate how fast it is going when the pushing force stops. That is a somewhat harder problem, but uses the same equation. You need to calculate the angular acceleration rate while it is being pushed, and multiply that by the time (15 seconds).
Use the same L/I equation, but in this accvelerating case, the torque is the difference of the pushing and frictional torques.
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