- #1
TimSon
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Homework Statement
Mass m whirls on a frictionless table, held to circular motion by a string which passes through a hole in the table. The string is pulled so that the radius of the circle changes from ri and rf.
a) show that the quantity L = mr^2(d(theta)/dt)
b) Show that the work in pulling the string equals the increase in kinetic energy of the mass
Homework Equations
F= ma where a is the acceleration in the radial direction
mg(ri - rh) = .5 * m * Vif^2 + .5*m*Vrf^2
The Attempt at a Solution
I first tried F = ma using the acceleration in terms of polar coordinates.
:x= second derivative of x
.x = second derivative of x
O = theta
-F = m(:r - r(.O)^2)
-F = m(r*.w - r(w)^2)
at this point i don't really know how to get from here since