Two blocks are sliding together along a frictionless surface. Block A, on the le

Question

Two blocks are sliding together along a frictionless surface. Block A, on the left, has a mass of 4.0 kg and block B, on the right, has a mass of 5.0 kg. Another object is exerting a force on B. The horizontal velocity as a function of time of both A and B is shown in the graph below (right is the positive direction). What is the horizontal force exerted by B on A? What is the force exerted on B by A? What is the force exerted by the other object on B? (Be sure to indicate direction with the sign.)

http://class.phys.psu.edu/WebAssign_figures/WebAssign_voft01.jpg

Explanation / Answer

from graph

v=m*t+c (m=slope of line& c=y intercept)

m=-4/5m/s2,c=6m/s

acceleration of both A & B=dv/dt=m=-4/5m/s2

fbd of combined A & B

f=(ma+mb)*a=9*-4/5=-7.2N

now for A

force on A exerted by B=f=ma*a=4*-4/5=-3.2N

by newton's law

force on B by A=3.2N

force on B by other object=-7.2N

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