A sound wave has a velocity of 342 m/s . It has a frequency of 621 Hz Find the wavelength

Consider a system to be two train cars traveling toward each other. what is the total momentum of the system before the train cars collide?   kg • what must the total momentum of the system be after the train cars collide?   kg •  

For the car in the picture ,in which direction is the normal force? -into the screen -down -out of the screen -up

Ball bearings are made by letting spherical drops of molten metal fall inside a talll tower-called a shot tower- and solidify as they fall. a-if a bearing needs 4.0 s to solidify enough for impact, how high must the tower be? b- what is the bearing's impact velocity?