A spring is an elastic object that stores mechanical energy. A spring scale is ready at

the airport to weigh luggage upon departure. Given the spring scale is 20 cm long and

reads from 0 to 60 N. Determine the potential energy of the spring when a passenger

weight his luggage during traveling:

1. when the luggage weight reaches 40 N,

2. when it stretched 20 cm, and

3. when the luggage in b)i contains an additional mass of 4 kg is suspended from

the spring