10. How much work is done when a ping pong ball of mass 40 kg speeds up from 6 m

Question

10. How much work is done when a ping pong ball of mass 40 kg speeds up from 6 m/s to 10 m/s in 45 seconds and travels 14 km? a)5x 10-2 J b) 5 x 102 J c) 5 x 104 J d) 5 x 10 J 11. Convert 4t/3 radians to degrees. 12. A physics textbook is dropped from 20 m and has a mass of 14 kg. What is its kinetic energy 5/9 of the way down? a) 2776 J b) 1666 J c) 1388 J d) 1524 J 13. If you lift a 500 N weight 3 m from the ground during a period of 4 seconds, how much work did you do? a) 1500 J b) 1300 W c) 1500 W d) 1300 J 14. Convert 78 degrees to radians. 15. Energy cannot be or a) transferred, lost b) created, destroyed c) conserved, transferred d) lost, gained

Explanation / Answer

10. Work = initial energy - final energy

W = KEi + UEi - KEf - UE f. v = u + at 10 = 6 +a*45

W = 1/2 * .40 * (102-62) + .40*4/45*14000 a = 4/45

W = 12.8 + 497.7 =510.5 J. Ans (b)

11. 4 pi / 3 = 4*180 /3 =240 degree

12. v2 =u2 + 2*a*s v2 =0 + 2*(-9.8)*20*5/9 v=14.757m/s

KE = 1/2 * 14 * 14.7572 = 1524 j . Ans(d)

13. W =f*s = 500 * 3 =1500 joule. Ans (a)

14. 78 degree = 78 * pi /180 = 13pi/30 =0.43 pi .Ans

15 b) created , destroy

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