A backpack full of books weighing 51.4N rests on a table in a physics laboratory classroom. A spring with a force constant of 140N/m is attached to the backpack and pulled horizontally.
Part A If the spring is pulled until it stretches 2.40cm and the pack remains at rest, what is the force of friction exerted on the backpack by the table? (N)
Part B Does your answer to part A change if the mass of the backpack is doubled? Explain