# Newton's Second Law and Friction

#### am13

1. The problem statement, all variables and given/known data

Block A weighs 1.14 and block B weighs 3.66. Block A rests on top of block B and has a cable connecting it to the wall on its right. The coefficient of kinetic friction between all surfaces is 0.300. Find the magnitude of the horizontal force necessary to drag block B to the left at constant speed if A is held at rest. (See Figure B)

2. Relevant equations

Fnet = ma
Ff=μN
Fnet = 0

3. The attempt at a solution

I think that I am just getting the forces on the free body diagram wrong. I drew FBDs for block B and block A and got that Fnet = 0, and so the horzontal force plus force friction by block A minus force friction by the ground equals 0. And I got F = FfG-FfA. What have I done wrong?

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#### rl.bhat

Homework Helper
Hi am13, welcome to PF.
The frictional force acting on A is towards right.
Reaction to this force on B acts towards left.
Applied force on B is towards left.
Frictional force on B acts towards...?
What is the condition for the constant velocity of B?

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