In Roger Hickey of California attained a speed of kmh while standing on a skateboard. Suppose Hickey is riding horizontally at his standup speed when he catches up to another skateboarder, who is moving at kmh in the same direction. If the second skateboarder steps sideways onto Hickeys skateboard, the two riders move forward with a new speed. Calculate this speed, assuming that both skateboarders have equal, but unknown, masses and that the mass of the skateboard is negligible.