問:有關力學

1.A body of weight 20N rests on a rough plane inclined at 20 to the horizontal, the coefficient of friction being 0.25.Find the force acting parallel to the line of greatest slope which will
(a)Cause the body juct to move up-plane,
(b)Just support the body.

thx

我唔明你1A問咩=.=
1B)︰
Let R be the normal reaction,F be the force needed to just support the body
resolve forces perpendicular to the inclined plane: R=20cos20
resolve forces parallel to the inclined plane: 20sin20=F+0.25R
substitute R into it
20sin20=F+0.25*20cos20
F=20(sin20-0.25cos20)

by the way,你呢科咩科黎ga??  CE physics定 AL apply maths??

1a
Required force = 0.25*20cos20+20*sin20

Coefficient of friction is not required in Hong Kong CE and AL Physics syllabus.