Brian is forced to help Stewie play on the swings at the park. He pushes Stewie until Stewie could reach a maximum height of 0.5 m above the lowest point on the swing and then stepped aside. Stewie gets scared of such a high height (considering he is very short) and decides to jump off the swings at the swings lowest point. If Stewie has a mass of 5 kg and the swing has a mass of 2 kg, what is the maximum height the swing will reach after Stewie jumps off with a velocity of 2 m/s?

So basically we want to think of this situation from the perspective of conservation of energy. As in, we can derive the velocity of both the swing and Stewie at the bottom of the swing via:

mgh = 0.5m*v^2

v = (2*g*h)^0.5 = (2*9.8*0.5)^0.5 = 3.13 m/s

This represents the velocity of Stewie and the swing at the bottom of the swing's path. Now, we will think of this from the perspective of conservation of momentum. Basically, the collective momentum of Stewie and the swing is equal to the sum of their subsequent momenta:

(5+2)*3.13 = 5*2+5*v(swing); v(swing) represents the velocity of the swing following Stewie jumping.

7*3.13 = 10 + 5v

v = 2.4 m/s

Now, we return to conservation of energy and find that the kinetic energy of the swing following Stewie jumping is equivalent to its final gravitational potential energy.

Based on the easily derivable formula: h=v^2/2g, we find that h = 2.4^2/19.6,

which is: 0.3 m.

If g is supposed to be 10 or you need a different degree of precision, then you can use my method. Hope this helps.