Work, Energy Momentum Question?

Question

Can an individual object have non zero momentum while the momentum of the entire system is zero?

I'd say yes because u might have same speed in opposite directions which would result in a zero momentum. Am i correct?

2) Why do roller coaster rides close down during rain? (Hint: Remeber conservation of energy and thermal energy)

I cant explain this one even with the hint

THANKS in advance guys

Answer 1

Your first answer is correct.  An example is two balls that are moving towards each other.  The net momentum can be zero while each ball has a non-zero momentum.

As for the second question, a roller coaster works when potential energy at the top is converted to kinetic energy (some energy is also lost as friction).  When it rains, energy will also be lost as the water is heated by friction, so the roller coaster may not have enough energy to make it to the end.