Posted by Lindsay on Tuesday, December 4, 2007 at 9:43pm.
A 5.70 kg block located on a horizontal floor is pulled by a cord that exerts a force F = 10.4 N at an angle theta = 27.5° above the horizontal. The coefficient of kinetic friction between the block and the floor is 0.10. What is the speed of the block 6.1 s after it starts moving?
I don't know how to do these equations in which they want you to find speed. A little help would be much appreciated.

Physics  Damon, Tuesday, December 4, 2007 at 10:24pm
This is a lot like your previous problem.
There is a force 10.4 cos 27.5 or 9.22 N horizontal from the cord.
There is a force 10.4 sin 27.5 or 4.80 N up from the cord
The force the block exerts down on the floor is the weight  the pull up from the cord
m g  4.80 N
= 5.70(9.8)  4.8 = 51.06 N normal to floor
So the friction force = .1 (51.06) = 5.11 N friction force
the net horizontal force on the block is therefore
9.22  5.11 = 4.11 N
now do F = m a
4.11 = 5.70 a
a = .721 m/s^2
initial speed o is 0 we assume
v = 0 + a t = .721 (6.1)= 4.4 m/s

Physics  Lindsay, Tuesday, December 4, 2007 at 10:29pm
Ohh ok great I understand.
Thanks a lot. :)
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