Forces on an inclined plane

given the folliwng information

the diagram attached shows a froce pulling a particel up an inclined slope. The force of -40j represents the weight of the particle and the frictional force down the slope has a mag of 65N.the displacement of the body AB, = (3i+4j)m. Calculate the frictional force in component form ai+bj.

just hoping sum1 could tell me how you are supposed to determine this...ie i know a^2+b^2=65^2 but i feel i am missing another variable in order to sub either a or b so that one of the 2 can be found...any help be be greatly appreciated!!! thanks

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ku1005 said:
given the folliwng information

the diagram attached shows a froce pulling a particel up an inclined slope. The force of -40j represents the weight of the particle and the frictional force down the slope has a mag of 65N.the displacement of the body AB, = (3i+4j)m. Calculate the frictional force in component form ai+bj.

just hoping sum1 could tell me how you are supposed to determine this...ie i know a^2+b^2=65^2 but i feel i am missing another variable in order to sub either a or b so that one of the 2 can be found...any help be be greatly appreciated!!! thanks
Set up some coordinate axis, and think about the angles and the relation between these angles and the vector components.

yeah i got it...soz...silly really (3i+4j) is opposite to but in line with the frictional force vector, hence ab value of (3i+4j)=5 therfore 65/5 * (-3i-4j) = (-32i-52j)N ....thanks