[ALI ALZAHRANI]

14. A 1-kg block is lifted vertically 1m by a boy. The work done by the boy is about: A. 1 ft · lb B. 1 J C. 10 J D. 0.1J E. zero ans: C

W = mgh cosQ = 1*9.8*1*cos180 = - 9.8 J

19. An 80-N crate slides with constant speed a distance of 5.0m downward along a rough slope that makes an angle of 30◦ with the horizontal. The work done by the force of gravity is: A. −400 J B. −200 J C. −69 J D. 200 J E. 400 J ans: D

W = mgsinQ *d = 80*5*sin30 = 200 J