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Summersnow8
 one year ago
Please help!
A bridge with mass 9000. kg supports a truck with mass 3000. kg that is stopped in the middle of the bridge. What mass (in kg) must each pier of the bridge support?
= (9000 kg + 3000 kg) / 2
= 6000 kg
If the truck in the preceding problems stops 9.00 m from the northern end of the 32.0m bridge, what mass (in kg) must the northern pier of the bridge support?
F1 + F2 = (9000 kg * 9.8 m/s^2) + (3000 kg * 9.8 m/s^2)
F1 + F2 = 88200 + 29400
F1 + F2 = 117,600 N
F1 (32.0 m) = (88200 N) (????? m) + (29400 N) (9.00 m)
@nikato @michele_Laino @lightgrav @radar @Greg_D @peachpi
the answers are suppose to be 5220 kg, 6580 kg
Summersnow8
 one year ago
Please help! A bridge with mass 9000. kg supports a truck with mass 3000. kg that is stopped in the middle of the bridge. What mass (in kg) must each pier of the bridge support? = (9000 kg + 3000 kg) / 2 = 6000 kg If the truck in the preceding problems stops 9.00 m from the northern end of the 32.0m bridge, what mass (in kg) must the northern pier of the bridge support? F1 + F2 = (9000 kg * 9.8 m/s^2) + (3000 kg * 9.8 m/s^2) F1 + F2 = 88200 + 29400 F1 + F2 = 117,600 N F1 (32.0 m) = (88200 N) (????? m) + (29400 N) (9.00 m) @nikato @michele_Laino @lightgrav @radar @Greg_D @peachpi the answers are suppose to be 5220 kg, 6580 kg

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anonymous
 one year ago
Best ResponseYou've already chosen the best response.0I tried this last night. Got the same numbers you did. 5220 kg doesn't even make sense for the first part because it's not enough support. The part you're missing for the 2nd part is 16 m. Weight acts at the center of the bridge, then you can solve for F1.

Summersnow8
 one year ago
Best ResponseYou've already chosen the best response.0@peachpi, yeah the answer for the first problem is 6000 kg, but there are 2 asnwers for the second problem... I need help with the second one only

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0Is there another question for the 2nd problem?

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0They only ask for mass as far as I can tell

Summersnow8
 one year ago
Best ResponseYou've already chosen the best response.0they are asking for the mass of the northern pier of the bridge.... so I don't know which answer it is or how you get the answers

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0dw:1437603862116:dw

Summersnow8
 one year ago
Best ResponseYou've already chosen the best response.0how do I figure out which one is north and which one is south?

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0North is the one closest to the truck. That's why I switched to N and S as subscripts to make it a little easier If you take the moment about the north side it's \[\sum M_N=(9~m)(29400~N)(16~m)(88200~N)(32~m)F_S=0\] Solving that gives the force on the south support

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0That should be + 32 Fs

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0For the north you can do the same, take the moment about the south end \[\sum M_S=(23~m)(29400~N)+(16~m)(88200~N)(32~m)F_N=0\]

Summersnow8
 one year ago
Best ResponseYou've already chosen the best response.0I got this: F1 (32.0 m) = (88200 N) (16 m) + (29400 N) (9.00 m) F1 (32.0 m) = 1675800 F1 = 1675800 / 32 m F1 = 52368

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0yeah that's what I got, then when you divide by 9.8 you'll get 5343.75 kg

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0that's for the south pier

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0for the north pier you can use the equation above or just subtract from 12000

Summersnow8
 one year ago
Best ResponseYou've already chosen the best response.0but the answers are 5220 kg & 6580 kg , not what we got

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0that's what I was saying above, those answers don't make sense. They don't even add up to 12,000 kg, which is the amount of mass that has to be supported

Summersnow8
 one year ago
Best ResponseYou've already chosen the best response.0well, those are the answers in the back of the book.... are you sure our equation is right? why do we divide by gravity? I am not understanding it

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0I divided by gravity because they asked for mass, not force. The equation is right. The answer makes no sense. The mass of the bridge and truck is 9000 + 3000 = 12000 kg. The answers for the supports are 5220 + 6580 = 11800 kg. This would mean the mass on the bridge is 200 kg more than it can support. Those answers cannot be right, unless something is missing from the problem

Summersnow8
 one year ago
Best ResponseYou've already chosen the best response.0I put the wrong answer, in the back of the book the problem is asking he mass must each pier of the bridge support, which the correct answer is 6000 kg

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0I'm confused. that's for the 1st question, right?

Summersnow8
 one year ago
Best ResponseYou've already chosen the best response.0sorry, i am confusing myself, yea that is for the 1st, but yeah the book says 5220 kg, 6580 kg for the second question...... I don't get it.....

Summersnow8
 one year ago
Best ResponseYou've already chosen the best response.0so did you get 5543.75 (south), and how do you solve for north?

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0You can set up a moment equation from the south side, like I did above. Or you can just subtract the south from 12000

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0since we know they have to add up to 12000

Summersnow8
 one year ago
Best ResponseYou've already chosen the best response.0so 6456.25 (north)

Summersnow8
 one year ago
Best ResponseYou've already chosen the best response.0okay, so the answer is 6460 ? I hope we solved this correctly :/

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0yeah ok if you round

Summersnow8
 one year ago
Best ResponseYou've already chosen the best response.0hmmm, okay. thanks for your help

mtimko
 one year ago
Best ResponseYou've already chosen the best response.0The correct answer (at least for my purposes) ended up being 6655 +/ 10
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