7. Friction, Inclines, Systems
Systems of Objects with Friction
2PRACTICE PROBLEM
Two wooden blocks are connected using an inelastic wire. The mass of block P is mP while block Q has a mass mQ. The blocks are placed on a horizontal bench. You pull the blocks to the left using a horizontal force F, giving the blocks a constant velocity. The blocks experience the same coefficient of kinetic friction, μk. Determine the magnitude of F in terms of mP, mQ, and μk with the help of one or more free-body diagrams.

Two wooden blocks are connected using an inelastic wire. The mass of block P is mP while block Q has a mass mQ. The blocks are placed on a horizontal bench. You pull the blocks to the left using a horizontal force F, giving the blocks a constant velocity. The blocks experience the same coefficient of kinetic friction, μk. Determine the magnitude of F in terms of mP, mQ, and μk with the help of one or more free-body diagrams.
ANSWERS OPTIONS
A
F = μkmQg
B
F = (mP - mQ)μkg
C
F = (mP + mQ)μkg
D
F = μkmPg
E
F = (mQ - mP)μkg