When a +3 n force is applied to this box, it does not move.

what is the frictional force on the box while the +3 n force is being applied?
a. less than -3 n
b. -3 n
c. between -3 n and 0 n
d. between 0 n and +3 n

answer: the potential energy decreases from 379 j to 243 j

explanation:

for the law of conservation of energy, the total energy in a system must be conserved. the total energy of the system is given by the sum of kinetic (k) and potential (u) energy:

e = k + u

the total energy is e=675 j, and this does not change.

initially, the kinetic energy is k=296 j, so the potential energy is

at the end, the kinetic energy is k=432 j, so the potential energy is

so, we see that the potential energy has decreased from 379 j to 243 j.