Posted by **Lindsay** on Sunday, January 13, 2008 at 3:52pm.

A flea pulls on a puck with force 7 microN at an angle of 30°. Another flea pulls on the puck with force 2 microN at an angle of -60°.

a) What is the magnitude of the net force on the puck? (I got 7.28 uN)

b)At what angle is the net force? ( I got about 14.07 deg)

c) A third flea decides to pull the puck so that it will stop accelerating. What is the magnitude of the force with which it must pull, and in what direction must the flea pull so that the puck stops accelerating?

This is the one I need help with. Is it similar to part a?

- Physics -
**Damon**, Sunday, January 13, 2008 at 4:11pm
a) sqrt(2^2+7^2) = sqrt(53) = 7.28 check

b)tan^-1 (2/7) = 15.9 and 30-15.9 = 14.1 check

c) you need the third flea to cancel the RESULTANT of a and b

He must pull at 7.28 *10^-6 N opposite to part b which is 14.1 + 180 = 194 degree(or 14.1 - 180)

- Physics -
**bobpursley**, Sunday, January 13, 2008 at 4:11pm
It depends on how the angle is measured. If the angle is measured from some arbritary axis, and the fleas are on the oppsite sides of this axis, then you have a ninety degree angle between the force vectors

You are correct on a, b. On C, the equilibrant force is equal and opposite to a.

I see it as 7.28uN at the angle opposite b.

- Physics -
**Damon**, Sunday, January 13, 2008 at 4:14pm
Ah, good, I am taking a break :)

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