Why is it easy to pull downwards

What color of light must blue light mix with to create white light? a. yellow b. white c. blue d. green

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?

Abox is sliding on a frictionless surface when it suddenly begins to rain heavily. if the downpour of rainfall falls vertically into the box