HELP PLEASE!
Scientist use different types of models to study the composition of matter and how matter behaves. Three different types of molecular models and their uses are shown. match each type of model with its use.

Explain the doppler effect in terms of frequency, wavelength, and speed.

Ben(55 kg) is standing on very slippery ice when junior(25kg) bumps into him. junior was moving at a speed of 8m/s before the collision and ben and junior embrace after the collision. find the speed of ben and junior as they move across the ice after the collision .

Which is not a characteristic of a heat pump? a. it is used in air conditioners. b. it uses a refrigerant. c. it requires no work. d. it reverses the normal flow of thermal energy.