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 U Font Family AA A E EED20. 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? O 1900 Nm O 770 Nm O 1300 Nm O 350 Nm13. 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? O 77% O 31% O 17% O 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? 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 ignned? O 1.4 m/s west 0 0.4 m/s east O 1.4 m/s east O 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? O -26 kg*m/s O -540 kg*m/s 26 kg*m/s 540 kg*m/s11. An scissor lift performs 9400 joules of work in a period of 2.4 seconds. How much power is the scissor lift producing? Q 9400 W O 3900 w 0 22,600 W O 450w \f18. Claudia is playing a game called bocce, which involves collisions between balls. She strikes a throws a 970 9 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 rst ball immediately after the collision? 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