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Energy quiz: 1) a) Friction “sucks out” all of the energy. Therefore, the KE at the bottom of the hill is equal to the work of friction on the flat section. 1 1 mv 20 − W f = mv 2 2 2 1 mv 20 − F f d = 0 2 1 µmgx = mv 20 2 − (0.35)(9.8)(17) = −(0.5)v 2 v = 10.8m / s b) 1 2 mv 2 1 2 1 kx + mgh = mv 2 2 2 1 1 (1000) x 2 + (3)(9..8)(1.7) = (3)(10.8 2 ) 2 2 x = 0.5m Us +Uk = 2) a) at x=0, U=0. Therefore, all 7 J of energy is found as kinetic energy. Therefore, 7=(0.5)mv2 but m=1 kg v=3.74m/s b) energy at x=0 must equal energy at =2 7=Ke+U 7=KE+-6 KE=13 J c) No, it does not have enough energy to reach x=-2 m. 3) D 4) C Ug = K 1 2 mv 2 1 9.8(.5) = v 2 2 v = 3.13m / s 2 mgh = 5) D Us + K = K 1 2 1 1 kx + mv 2 = mv 2 2 2 2 1 1 1 (80)(.04) 2 + (.5)(.5) 2 = (.5)v 2 2 2 2 v = 0.71m. / s 6) D 7) B