The drawing shows box 1 resting on a table, with box 2 resting on top of box 1.
ID: 2142056 • Letter: T
Question
The drawing shows box 1 resting on a table, with box 2 resting on top of box 1. A massless rope passes over a massless, frictionless pulley. One end of the rope is connected to box 2, and the other end is connected to box 3. The weights of the three boxes are W1 = 51.5 N, W2 = 39.0 N, and W3 = 25.3 N. Determine the magnitude of the normal force that the table exerts on box 1.
The drawing shows box 1 resting on a table, with box 2 resting on top of box 1. A massless rope passes over a massless, frictionless pulley. One end of the rope is connected to box 2, and the other end is connected to box 3. The weights of the three boxes are W1 = 51.5 N, W2 = 39.0 N, and W3 = 25.3 N. Determine the magnitude of the normal force that the table exerts on box 1.Explanation / Answer
So assuming box 2 and 3 aren't touching.
The forces on box 2 are:
Force of gravity
Force of tension
Normal force
The box isn't accelerating so
T + N2 - Fg2 = 0
The forces on box 3 are:
Force of gravity
Tension
Since box 3 isn't accelerating
T - Fg3 = 0
The tension force is equal in both cases so:
Fg3 + N2 - Fg2 = 0
So N2 = Fg2 -Fg3
N2 = Fg2 - Fg3 = (39)-(25.3) = 13.7 N
Remember forces are equal and opposite.
Now write the equation for the forces acting on Block 1
There is the force of gravity
There is the normal force from the table and
A force equal and opposite to the normal force on block 2 so...
N1 - Fg1 - N2 = 0 (since block 1 isn't accelerating)
N1 = Fg1 +N2
N1 = 51.5 + 13.7 = 65.2 N
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