-- Posted by Anonymous at 3:26 am on Nov. 20, 2008 Brutus, a champion weightlifter, raises 221 kg of weights a distance of 2.45 m. How much work is done by Brutus lifting the weights? I can't figure it out, because I thought Work= Force x Distance. But the force isn't given here. But doesn't F= mass x acceleration? but there's no acceleration here? And I know the answer isn't 0. *confused* -- Posted by Rollo Tomasi at 3:27 am on Nov. 20, 2008 acceleration is 9.8 m/s^-2 -- Posted by Rollo Tomasi at 3:28 am on Nov. 20, 2008 you know...gravity? -- Posted by Anonymous at 3:28 am on Nov. 20, 2008 Quote: from Rollo Tomasi at 3:27 am on Nov. 20, 2008 acceleration is 9.8 m/s^-2 Are you saying the acceleration is negative? I see a -2 there. -- Posted by Rollo Tomasi at 3:29 am on Nov. 20, 2008 ...god damn son, you need a lot more help than i can give you -- Posted by JohnTheNormalOne at 3:29 am on Nov. 20, 2008 the answer is 42 -- Posted by Anonymous at 3:29 am on Nov. 20, 2008 Quote: from Rollo Tomasi at 3:29 am on Nov. 20, 2008 ...god damn son, you need a lot more help than i can give you Leave. -- Posted by Rollo Tomasi at 3:31 am on Nov. 20, 2008 i will, but i take comfort knowing that only one of us here is stupid. and because i know you won't be able to figure out which one of us it is, i am also here to tell you that it is you who is stupid. hth. -- Posted by Killtyronedead at 3:36 am on Nov. 20, 2008 Quote: from Anonymous at 6:28 am on Nov. 20, 2008 Quote: from Rollo Tomasi at 3:27 am on Nov. 20, 2008 acceleration is 9.8 m/s^-2 Are you saying the acceleration is negative? I see a -2 there. Wow.  You're not very bright. -- Posted by FurryPanther at 3:37 am on Nov. 20, 2008 Gravity is acceleration in the direction opposite the one of motion, namely down when the weight is moving up. W = F x d F = m x a Therefore: W = m x a x d W = 221kg x 9.8m/s^2 x 2.45m Also, Rollo Tomasi's notation is correct. W = 221kg x 9.8ms^-2 x 2.45m This results in: W = 5306.21 J W = 5.3 kJ There you go. That was immensely simple. I think you need a tutor. Badly. FP -- Posted by roflfuckyou at 3:45 am on Nov. 20, 2008 i get 5306.21J as the work don't know if it's right though. -- Posted by FurryPanther at 3:46 am on Nov. 20, 2008 Quote: from roflfuckyou at 4:45 am on Nov. 20, 2008 i get 5306.21J as the work don't know if it's right though. That's right. 5.3kJ with significant figures. FP -- Posted by roflfuckyou at 3:47 am on Nov. 20, 2008 yeah i just did sum of the forces = m x a a = gravity m = 221kg then i did w = f x d f = 2165.8 d = 2.45 so work = 5306.21j -- Posted by Fishboner at 3:55 am on Nov. 20, 2008 The OP fails at math. -- Posted by roflfuckyou at 3:59 am on Nov. 20, 2008 Quote: from FurryPanther at 10:46 pm on Nov. 20, 2008 Quote: from roflfuckyou at 4:45 am on Nov. 20, 2008 i get 5306.21J as the work    don't know if it's right though. That's right. 5.3kJ with significant figures. FP yay i retained something from a years work of physics (: -- Posted by Krebons at 11:41 am on Nov. 20, 2008 Okay, if ur under 14, then in most exams, gravity is taken to be 10 Which is alot easier So 10x221 = 2210 2210 x 2.45 = 5414.5 J I think