400N magnitude of the friction acting on the crate.
work done by gravity
[tex][w=mg sin \theta \cdotS],[w=mgh=],[w=800 \cdot2=w=1600][/tex]
Then was done by friction external work - wask done by gravity
[tex][f_S \cdot S=3200-1600],[f_S \cdot4=1600],[f_S=400 N][/tex]
Thus the crate is not moving with constant speed then we can say that the value of friction Force is less then 400 N
So Friction Force is not zero but less then the 400N
The resistance present at the contact surface at the point of contact when two or more objects move over one another can be referred to as friction force. The direction of friction force is always perpendicular to the object's motion.
The amount of friction is influenced by the surface's roughness and outside pressures. The force of friction works more strongly on a surface the rougher it is. The same is true of outside factors.
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