Hi! I have a two-part problem to solve. I think I solved it but in the class the professor told us that there's something wrong with the exercise. The spring constant of a toy dart gun is 1350 N/m. To cock the gun the spring is compressed 1 cm (0.01 m). The 5g (0.005 kg) dart, fired straight upward, reaches a maximum height of 24 m. g is 9.81 m/s^2. Determine the energy dissipated by air friction during the dart's ascent. My solution: E = -1/2 *(k) *(x)^2 + m*g*h =-0.5*1350* (0.01)^2 + 0.005*9.8*24 = -0.0675 + 1.176 = 1.1085 J Part 2. What speed should the projectile have when it returns to its starting point? Solution: m*g*h = 0.5*m*v^2 v = sqrt(2*g*h) =sqrt(470.4) = 21.69 m/s These make sense to me, but i don't know why the professor told me there's something wrong in the problems.