Answer:
v = 12,4 m/s
Explanation:
frictionless means all gravitational Energie (Eg) will be converted to kinetic Energie (Ek)
Ek = 0.5 * m * v^2
Ez = m * g * h
Ek = Ez
0.5 * m * v^2 = m * g * h
divide left and right of the = sign by m.
(This means that the final velocity is independent of the mass of both children !)
0.5 * v^2 = g * h
v^2 = 2 * g * h
v = +- SQRT (2 * g * h)
with
g = 9.8 m/s^2
h = 7,8 m/s
v = +- SQRT (2 * 9.8 * 7.8)
v = +- SQRT (152.88)
(v = - 12,4 m/s has no meaning in this case)
The velocity 7,8 m below the starting point, will be
v = 12,4 m/s
