Free Body Diagram Physics Example 2

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Example 2

medium
A 5 kg5 \text{ kg} block is pulled across a rough surface (μk=0.2\mu_k = 0.2) by a 30 N30 \text{ N} horizontal force. List all forces in the free-body diagram and find the acceleration. Use g=9.8 m/s2g = 9.8 \text{ m/s}^2.

Solution

  1. 1
    Forces in the FBD: weight W=mg=49 NW = mg = 49 \text{ N} (down), normal force N=49 NN = 49 \text{ N} (up), applied force F=30 NF = 30 \text{ N} (right), friction fk=μkN=0.2×49=9.8 Nf_k = \mu_k N = 0.2 \times 49 = 9.8 \text{ N} (left).
  2. 2
    Net horizontal force: Fnet=30−9.8=20.2 NF_{\text{net}} = 30 - 9.8 = 20.2 \text{ N}.
  3. 3
    Acceleration: a=Fnetm=20.25=4.04 m/s2a = \frac{F_{\text{net}}}{m} = \frac{20.2}{5} = 4.04 \text{ m/s}^2

Answer

a≈4.04 m/s2a \approx 4.04 \text{ m/s}^2
A free-body diagram for a block on a rough surface includes four forces: weight, normal force, applied force, and friction. The FBD helps organize forces before applying Newton's second law.

About Free Body Diagram

A simplified diagram that isolates a single object and represents all external forces acting on it as labelled arrows originating from the object's centre of.

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