We have two a pulley system with two masses of 2kg and 3kg on two ends of a massless string. At the end of 5 seconds, the string breaks. How far up did the 2kg block move?
Here's what I have tried:- $$a_{net}=\frac{F_{net}}{m_1+m_2}$$ $$a_{net}=\frac{3g-2g}{3+2}$$ $$a_{net}=1.96m/s^2$$ $$v=u+at$$ $$v=0+(1.96)(5)$$ $$v=9.8m/s$$ Now the 2kg block moved with velocity 9.8m/s till the string broke, so all the kinetic energy during this travel converted to potential energy
$$PE=\frac{1}{2}mv^2$$ $$PE=96.04J$$ $$mgh=96.04J$$ $$h=4.9m$$
So this happens to be the correct answer but I wanted to use an alternative method which should work but isn't:- $$S=\frac{1}{2}at^2$$ $$S=\frac{1}{2}(1.96)5^2$$ $$S=24.5m$$
Can someone explain why using the basic kinematics equation doesn't work?