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catsrule332
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A 25 kg block is at rest on a horizontal surface. A horizontal force of 75 N is required to set the block in motion. When it is in motion a 60 N forced is required to keep the block moving with a constant speed. Find the coefficients of static and kinetic friction. Draw a force diagram and explain!
 2 years ago
 2 years ago
catsrule332 Group Title
A 25 kg block is at rest on a horizontal surface. A horizontal force of 75 N is required to set the block in motion. When it is in motion a 60 N forced is required to keep the block moving with a constant speed. Find the coefficients of static and kinetic friction. Draw a force diagram and explain!
 2 years ago
 2 years ago

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salini Group TitleBest ResponseYou've already chosen the best response.0
so catsrule wat have u figured out so far in this question?
 2 years ago

catsrule332 Group TitleBest ResponseYou've already chosen the best response.0
find normal force: n=mg=(25)(9.8)= 245 N \[f=m*\eta\]dw:1333113193720:dw
 2 years ago

JamesJ Group TitleBest ResponseYou've already chosen the best response.2
When the object is not moving, the maximum frictional force on the block is the static friction. Static friction is given by \[ Fr_S = \mu_S N \] where \( \mu_S \) is the coefficient of static friction. Now which force in the problem is that equal to?
 2 years ago

salini Group TitleBest ResponseYou've already chosen the best response.0
u are in the right track wat is the expression for frictional force with normal reaction? and do u know the difference abt coefficient of static friction and kinetic friction?
 2 years ago

JamesJ Group TitleBest ResponseYou've already chosen the best response.2
On the other hand, once the object is moving, the maximum frictional force is the kinetic friction and that is given by \[ Fr_K = \mu_K N \] where \( \mu_K \) is the coefficient of kinetic friction and of course \( N \) is the normal force. What value is the kinetic friction equal to in this problem?
 2 years ago

salini Group TitleBest ResponseYou've already chosen the best response.0
cats rule james has given everything needed for the sum u have to get the answer using that
 2 years ago

catsrule332 Group TitleBest ResponseYou've already chosen the best response.0
Static friction: fsmax=\[\mu *\eta\] Kinetic friction: fk=\[\mu * \eta\] 75/(25)(9.8)= .31 N 60/245) =.24 N
 2 years ago

JamesJ Group TitleBest ResponseYou've already chosen the best response.2
Yes, the coefficient of static friction is 0.31. Notice that these coefficients are unitless, because you have Newtons on both sides of the equation \( F = \mu N \) and force of friction \( F \) and the normal force \( F \) both have units of Newtons.
 2 years ago
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