A vertically hanging spring has a mass of 50 N hanging from it. Under these conditions, the spring stretches 10 cm. The spring is then placed on a horizontal table and stretched 20 cm. What force is required in the second scenario?
k•x1=m•g
k=m•g/x1=50/0.1=500 N/m
F= k•x2=500•0.2=100 N.