Two boys on skates push off from each other. the 40 kg boy moves to the left at 10 m/s. if the other boy moves to the right at 8 m/s, what is his mass?

Consider a system with two masses that are moving away from each other. why will the kinetic energy differ if the frame of reference is a stationary observer or one of the masses?

Aspring is used to stop a 50-kg package which is moving down a 20º incline. the spring has a constant k = 30 kn/m and is held by cables so that it is initially compressed 50 mm. knowing that the velocity of the package is 2 m/s when it is 8 m from the spring and neglecting friction, determine the maximum additional deformation of the spring in bringing the package to rest.

Awave with a frequency of 500 hz is traveling at a speed of 100 m/s. what is the wavelength?