Step 1: Understanding the Question: We need to determine the Shear Force Diagram (SFD) for a cantilever beam with a point load and a couple (moment) applied at the midpoint.
Step 2: Analyzing the Loads and Reactions: - Support: Fixed at the left end (\(x=0\)).
- Loads at \(x = L/2\): Point load \(P\) (downward), Moment \(M\) (clockwise).
- Reaction at Support (\(x=0\)): From vertical force equilibrium \(\Sigma F_y = 0\): \[ R_A - P = 0 \Rightarrow R_A = P \, (\text{upwards}) \]
Step 3: Constructing the SFD: Shear Force \(V(x)\) is the sum of vertical forces to the left (or right) of the section.
- Region \(0<x<L/2\): Looking to the left, the only force is the support reaction \(R_A = P\) (upwards). \[ V(x) = +P \] The diagram is a horizontal line (rectangle).
- At \(x = L/2\): There is a downward point load \(P\). The shear force drops by \(P\).
- Region \(L/2<x<L\): \[ V(x) = +P (\text{Reaction}) - P (\text{Load}) = 0 \] The shear force is zero in this section.
Step 4: Effect of the Moment \(M\): A concentrated moment affects the Bending Moment Diagram (BMD) by creating a vertical jump, but it
does not affect the Shear Force Diagram directly. Therefore, the moment at \(L/2\) causes no change in the SFD shape.
Step 5: Conclusion: The SFD consists of a rectangle of magnitude \(P\) from the fixed end to the midpoint, and zero thereafter.