My questions: (in order of attached images) 1. Why doesn't the vertical component of P affect the mass of the lawnmower? Why isn't the mass = mass of lawnmower + (Psin40)/g? 2. This question, I totally have no idea how it should be calculated. I tried by labelling the weight at the exact middle of the plank, then divide the 120N into two, each for one stool. Then I divide the 80N into two. Then I calculated the moment for each stool by multiplying the distances and the forces. But apparently that's not how it should be done :shy: Does a reaction force act on that object? 3. Using the formula E= stress/strain, Stress= F/A = 75/ (0.25∏d^2) =1.1 x 10^6 Pa Strain = (extension,x)/1.8 Adding the Young modulus together = 3.3 x 10^11 so by arranging everything in the formula, I found x = 6 x 10^-6 which is not the answer. What's wrong?