Block A in the fig. 5.58 weighs 1.20N and Block B weighs3.60N.

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Block A in the fig. 5.58 weighs 1.20N and Block B weighs3.60N. The Coefficient of kinetic friction between all surfaces is0. 300. Find the magnitude of the horizontal force F necessary to drag black B to the left at a constant speed a) if A rest on B and moves with it (fig. 5.28am). b) If A is held at rest.

2020-10-19
a) The most direct way to do part (a) is toconsider the blocks as a unit, with total weight 4.80 N. Then thenormal force between block B and the lower surface is 4.80N, and the friction force that must be overcome by the force F is $$\displaystyle{.3}\cdot{4.8}={1.44}{N}\to{t}{h}{r}{e}{e}{f}{i}{g}{u}{r}{e}{s}.{b}{)}{T}{h}{e}{\left\|{a}\right\|}{l}{f}{\quad\text{or}\quad}{c}{e}{b}{e}{t}{w}{e}{e}{n}{b}{l}{o}{c}{k}{B}{\quad\text{and}\quad}{t}{h}{e}{l}{o}{w}{e}{r}{s}{u}{r}{f}{a}{c}{e}{i}{s}{s}{t}{i}{l}{l}{4.80}{N},{b}{u}{t}{\sin{{c}}}{e}{b}{l}{o}{c}{k}{A}{i}{s}{m}{o}{v}\in{g}{r}{e}{l}{a}{t}{i}{v}{e}\to{b}{l}{o}{c}{k}{B},{t}{h}{e}{r}{e}{i}{s}{a}{\mathfrak{{i}}}{c}{t}{i}{o}{n}{f}{\quad\text{or}\quad}{c}{e}{b}{e}{t}{w}{e}{e}{n}{t}{h}{e}{b}{l}{o}{c}{k}{s},{o}{f}{m}{a}{g}{n}{i}{t}{u}{d}{e}{P}{S}{K}{.3}\cdot{1.2}={.360}$$ N so the total frictionforce F must overcome 1.44+.36=1.8N

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