As we know that spring potential energy is given by the formula
[tex]U = \frac{1}{2}kx^2[/tex]
now it is given to us that
[tex]U = 3500 J[/tex]
[tex]x = 1.5 m[/tex]
now we will plug in data in above equation
[tex]3500 = \frac{1}{2} k(1.5)^2[/tex]
[tex]k = \frac{2 \times 3500}{1.5^2}[/tex]
now we will have
[tex]k = 3111 N/m[/tex]
