A mass 3m collides head-on with a mass m. Before the collision the masses are moving directly toward one another with the same speed v0. After the collision, the mass 3m is moving in its original direction at speed v0/2. What is the speed v of the mass m after the collision

One soccer player (a) is moving at 4 km/h when she kicks the ball while another soccer player (b) is moving at 8 km/h. what statement accurately compares their kinetic energy if they have the same mass? a) both soccer players have the same kinetic energy. b) player b has twice the kinetic energy of player a. c) player b has four times the kinetic energy of player a. d) their kinetic energy can't be compared without knowing their mass.