Problem 5.76 Block A in the figure weighs 1.70N and block B weighs 2.60N . The c

Question

Problem 5.76 Block A in the figure weighs 1.70N and block B weighs 2.60N . The coefficient of kinetic friction between all surfaces is 0.500. Part A Find the magnitude of the horizontal force vector Fa necessary to drag block B to the left at a constant speed of 8.00cm/s if A rests on B and moves with it (figure a). Fa= Part B Find the magnitude of the horizontal force vector Fb necessary to drag block B to the left at a constant speed of 8.00cm/s if A is held at rest by a string (figure b). Fb = Part C In part (A), what is the friction force on block A?

Explanation / Answer

so for bottom block

F - frictiontop - friction bottom = mA a

for top top block

friction top = mb a

since constant speed a = 0

so friction top = 0

then F = friction bottom = 0.5*(1.7+2.6)= 2.15 N

b)

now top block

friction - T = 0

now friction is kinetic not static

so friction = u N = u mb g

still a = 0

so F = frictiontop + friction bottom = 2.15 + 0.5*1.7= 3 N

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