PLS HELP FOR PHYSICS PLS

Will give brainliest! jay rides his 2.0-kg skateboard. he is moving at speed 5.8 m/s when he pushes off the board and continues to move forward in the air at 5.4 m/s. the board now goes forward at 13 m/s.a. determine jay’s mass.b. determine the change in the internal energy of the system during this process.(express your answer to two significant figures and include the appropriate units.)

Matter is needed to transfer thermal energy bya. conductionb. convectionc. radiation d. both a & b.

The frequency of the fundamental of the guitar string is 320 hz. at what speed v do waves move along that string?