In the figure we see two blocks connected by a string and tied to a wall, with ?
ID: 1981467 • Letter: I
Question
In the figure we see two blocks connected by a string and tied to a wall, with ? = 32°. The mass of the lower block is m = 0.9 kg; the mass of the upper block is 2.0 kg.
(a) Find the tension in the string connecting the two blocks. ____ N
(b) Find the tension in the string that is tied to the wall. ____ N
THEN
Two blocks are connected by a string, as shown in the figure. The smooth inclined surface makes an angle of ? = 44° with the horizontal, and the block on the incline has a mass m1 = 7.3 kg. Find the mass m2 of the hanging block that will cause the system to be in equilibrium. (The pulley is assumed to be ideal.) ___ kg
Explanation / Answer
If we assume that the plane is frictionless - generally a terrible assumption, but what the heck - then the tension in the string connecting the blocks will be the parallel component of the weight of 0.8 kg. That will be mg sin(31). The tension in the string connected to the wall will be the parallel component of the weight of 2.8 kg. Again, mg sin(31). If there's friction with the plane, then you don't have enough information to get a numeric answer. You'll have to take the answers above and subtract off the friction: in the first case, that will be u mg cos(31) (u = mu, the coefficient of friction). In the second case, it'll be that minus another u mg cos(31).
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