Problem 1:(adsbygoogle = window.adsbygoogle || []).push({});

A box of books weighting 300 N is shoved cross the floor of an apartment by a force of 400 N exerted downward at an angle of 35.2* below the horizontal. If the coefficient of kinetic friction between box and floor is .57, how long does it take t move the box 4 m, starting from rest ?

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w = 300 N ==> m = 30.6 kg

u (coefficient)= .57

d = 4m

v0= 0

F (f) = u time F (normal)

F (normal) is the same as F (perpendicular)

F (per) = 300 cos 35.2* = 245.1 N

F (f) = .57 time 245.1 = 139.7 N

F = ma

139.7 = 30a --> a = 4.6 m/s2

V(final) = 2ad = 36.8 m/s

From vf = vi + at --? t = 8s

What i did wrong ?

Problem 2:

A box slides down a 30* ramp with an acceleration of 1.2 m/s2. Determine the coefficient of kinetic friction between the box and the ramp.

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Can some one give me some hints ?

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# Homework Help: Coefficient of friction of box of books

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