Answer:
Force required, F = 20 pounds
Step-by-step explanation:
We have given,
force needed to stretch a spring , F = 12 pounds
Stretched length, x = 9 inches
Since, spring force formula can be given as: F = kx
i.e 12 = k · 9
or k = = 4/3
Now we need to find force for the stretch length = 15 inches
i.e F = kx , here x =15inches , k = 4/3 and F= ?
or F = (4/3) · 15
or F = 20 pounds
Hence force required, F= 20 pounds