IIT JEE , AIEEE Forum - Physics , Mechanics - i have so many doubts in friction,hc verma........

waterdemon

29)

The Force which may cause the tendency of motion or the
motion in the body is its own Weight & the applied horizontal
force of 15N.

We have Resultant of the forces as:
F_res =

(20)²+(15)²
F_res =

625
F_res = 25N.

In a Direction of:
@ = Tan^-1(15/20) = Tan^-1(3/4) = 37⁰ with the Vertical.

The Friction will always oppose the tendency of Relative
motion and will act in a direction opposite of Resultant F.
F = Force.

Now for the acceleration to be minimum:
Minimum Force required: (N=40=F applied against the wall)
F_min = F - uN
F_min = 25 - (0.5)40
F_min = 5N.

So the minimum Acceleration will be:
F_min=ma_min
5 = 2(a_min)
a_min = 2.5m/s².

Since @ = 37⁰ with the vertical so @ = 53⁰ with the
Horizontal.

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Cheers!!!!!!!!!!!!!

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