Two Blocks on Inclined plane

“Physics Principles with Applications”, Douglas C. Giancoli, 7th Edition, Global Edition

44. Two blocks are connected by a light string passing over a pulley of radius 0.15 m and moment of inertia I. The blocks move (toward the right) with an acceleration of 1.00 m/s2 along their frictionless inclines (See figure below). (a) Draw free-body diagrams for each of the two blocks and the pulley. (b) Determine FTA and FTB, the tensions in the two parts of the string. (c) Find the net torque acting on the pulley, and determine its moment of inertia, I.

Giancoli 8-44

Analyze the problem:

The problem has two blocks on inclined surfaces and they are attached by an inelastic string (so they should have the same acceleration) the pulley’s mass is not ignored (we know that because the problem mentioned that there is a moment of inertia).

What are the given information?

  1. Block A mass, mA=8 kg
  2. Block B mass, mB=10 kg
  3. Acceleration, a = 1 m/s2
  4. Inclination Angle 1, θ1=32º
  5. Inclination Angle 2, θ2=61º
  6. Radius of pulley, R= 0.15 m

What are the needed information?

  1. Body-diagram draw for the two blocks and the pulley.
  2. FTA and FTB tension forces
  3. The net torque on the pulley
  4. The moment of inertia of the pulley


Giancoli 8-44-1

Giancoli 8-44-2