- #1
Bestfrog
Homework Statement
A massless string of length 2l connects two hockey pucks that lie on frictionless ice. Aconstant horizontal force F is applied to the midpoint of the string, perpendicular to it (see right figure). How much kinetic energy is lost when the pucks collide, assuming they stick together?
The Attempt at a Solution
Putting a y-axis along the string when it is straight and a x-axis along the direction of the force, the force acting on the puck "at the bottom" along the t-axis is ##\frac{F}{2}\cdot tan \theta##.
So, by calculating the work for this puck I obtain ##W=\int_{-l}^{0} \frac{F\cdot tan \theta}{2}dy=\int_{-l}{0} \frac{F\cdot tan \theta}{2} d(l\cdot sin\theta)= \int_{\frac{-\pi}{2}}^{0} \frac{Fl}{2}\cdot sin\theta d\theta##.
Can you explaine me how the last passage works?