The cars of an amusement-park ride have a speed v1 = 90 km/h at the lowest part of the t...

The cars of an amusement-park ride have a speed v₁ = 90 km/h at the lowest part of the track. Determine their speed v₂ at the highest part of the track. Neglect energy loss due to friction. (Caution: Give careful thought to the change in potential energy of the system of cars.)