GS-1 Physical Sciences Question 26

[amy_gumm2723]

why do you not account for gravitational force on the smaller mass as well?

[mcat_premed3832]

Gravitational force is definitely accounted for in the smaller mass. The weight of the small mass is 10 N which = mg. Thus the weight incorporates the gravitational force. If only the mass was given, then you would have had to multiply the mass by g.

[catherine_5701]

how does this fit in with the formula Ff=(mu static)x normal force? -- Mu static is not given, but the normal force of the big block on the table is 200N..

[mcat_premed3832]

There are 2 things that you must keep in mind:

1) the equation that you gave involving mew and the normal force, is not just the equation for frictional force; we must specify the following: it is the equation for maximal frictional force (you might want to see the video on Friction to clarify the difference).

2) the frictional force acts on the 200 N mass to the left which is in opposition to the applied force that acts to the right. Because the mass is not moving, the frictional force in this problem must be below the maximal frictional force which can be calculated with the equation that you provided.