15. While high efficiency is a goal of most machines, perfect efficiency is not actually attainable. As a result, the work done on the machine is greater than the work the machine outputs. Does this inefficiency violate the law of conservation of energy? Why or why not? B i U Font Family AA A 20. Harrison is holding on to a tree branch. The branch is angled 15 below horizontal. If Harrison weighs 640 N, and he is holding onto the branch 2.1 m away from the trunk, how much torque is he exerting on the tree? 1900 Nm 770 Nm 1300 Nm 350 Nm 13. Wanda is driving a screw into a plank of wood. She does 44.6 J of work on the screw, and the screw does 13.9 J of work on the wood. What is the efficiency of the screw Wanda is using? 77% 31% 17% 54% 17. Tasha is using a wedge to split wood. The wedge gives her a mechanical advantage of 4.8. How much force will Tasha need to exert, if it requires 770 N of force to split the wood? 990 N 3700 N 480 N 160 N 12. A trail maintenance crew is blowing up a boulder, to remove it from the trail. When they ignite the charge, the boulder splits in two. One side has a mass of 496 kg, and moves east with a velocity of 0.4 m/s. The other side has a mass of 145 kg. What is the velocity of the 145 kg side after the charge is ignited? 1.4 m/s west 0.4 m/s east 1.4 m/s east 0.4 m/s west 14. Two people are inline skating on the sidewalk. The first person has a mass of 71 kg, and is skating south at a speed of 3.6 m/s. The second person has a mass of 60 kg, and is skating north at a speed of 4.7 m/s. If these two people were to collide, what would their combined momentum be after the collision? -26 kg*m/s O-540 kg*m/s 26 kg*m/s 540 kg*m/s 11. An scissor lift performs 9400 joules of work in a period of 2.4 seconds. How much power is the scissor lift producing? 9400 W 3900 W 22,600 W 450 W 16. How much work can a 2.24 kW motor perform in a period of 0.33 s? 6800 J 740 J 2240 J 98 J 18. Claudia is playing a game called bocce, which involves collisions between balls. She strikes a throws a 970 g ball with a velocity of 7.0 m/s east. This ball strikes a stationary ball that also has a mass of 970 g. After the collision, the seconds ball travels with a velocity of 6.2 m/s east. What is the velocity of the first ball immediately after the collision? 0.50 m/s 0 m/s 6.2 m/s 0.80 m/s 19. Two balls of clay are launched into the air. One, which has a mass of 0.75 kg, travels north at a speed of 11.0 m/s. The other, which has a mass of 0.40 kg, travels south at a speed of 14.4 m/s. When the two balls collide, they fuse to form a single unit. What is the velocity of the single unit? 2.1 m/s -1.7 m/s 1.7 m/s 12 m/s