Question

Which of these would be an example of unbalanced forces?

Answer 1

Your answer is:

D. A snowball picks up speed as it rolls down the mountain.

An unbalanced force is when 2 forces act on each other (they aren't equal and opposite). That makes them cause motion.

Answer 2

A snowball picks up speed as it rolls down the mountain. (D)

Since the description includes acceleration ("picks up speed"), we know that the forces on the snowball must be unbalanced.