Difficulty: Easy
Correct Answer: 50 N at each end
Explanation:
Introduction / Context:
A floating log subjected to a concentrated load behaves, in a first approximation, like a simply supported beam with equal reactions provided by buoyancy on either side of the load. Recognizing the reaction distribution allows quick identification of shear force magnitudes.
Given Data / Assumptions:
Concept / Approach:
For a simply supported beam with a central point load W, the end reactions are equal: R_A = R_B = W/2. The maximum positive/negative shear magnitude equals the reaction magnitude and occurs just to the left/right of the midspan or at the supports in the shear force diagram.
Step-by-Step Solution:
W = 100 N at midspan → reactions R_A = R_B = W/2 = 50 N.Shear diagram jumps from +50 N near the left support to −50 N near the right support at the load location.Maximum absolute shear magnitude = 50 N at each support region.
Verification / Alternative check:
Equilibrium: ΣV = R_A + R_B − W = 50 + 50 − 100 = 0; ΣM about any support confirms R = W/2.
Why Other Options Are Wrong:
Common Pitfalls:
Confusing support shear with bending moment; mixing total load with reaction magnitudes.
Final Answer:
50 N at each end
Discussion & Comments