The doppler effect is the change in observed frequency due to
a. the type of medium the wave is in
b. the type of wave
c. the original frequency of the source
d. the motion of the source or observer

A12-g wad of sticky clay is hurled horizontally at a 100-g wooden block initially at rest on a horizontal surface. the clay sticks to the block. after impact, the block slides 7.5 m before coming to rest. if the coefficient of friction between the block and the surface is 0.65, what was the speed of the clay immediately before the impact?