A cantilever beam of the square section is subjected to a load W at t...
A cantilever beam with a square cross-section of 6 mm side is subjected to a load of 2 kN normal to the top surface, as shown in the figure. Young's modulus of elasticity of the material of the beam is 210 GPa. The magnitude of slope ( in radian) at Q (20 mm from the fixed end)
View all questions of this test
A cantilever beam of the square section is subjected to a load W at t...
Given:
- Cantilever beam of square section
- Load W applied at the free end
- Length of the beam is doubled
- Load is reduced to half
To Find:
The ratio of deflection at the free end after doubling the length of the beam and reducing the load to half compared to the original deflection.
Solution:
Step 1: Calculate the deflection of the original beam
The deflection of a cantilever beam can be calculated using the formula:
δ = (WL^3)/(3EI)
Where:
- δ is the deflection at the free end
- W is the load applied at the free end
- L is the length of the beam
- E is the modulus of elasticity
- I is the moment of inertia of the beam section
Since the beam is of square section, the moment of inertia (I) can be calculated using the formula:
I = (b^4)/12
Where:
- b is the side length of the square beam section
Let's assume the original length of the beam is L and the original deflection is δ1.
Step 2: Calculate the deflection after doubling the length and reducing the load
The new length of the beam is 2L and the new load is W/2. Let's assume the new deflection is δ2.
Using the formula for deflection, we can write:
δ2 = ((W/2)(2L)^3)/(3EI)
Simplifying the equation:
δ2 = (W*L^3)/(3EI)
Step 3: Calculate the ratio of deflections
Now we can calculate the ratio of deflections by dividing the new deflection (δ2) by the original deflection (δ1):
Ratio = δ2/δ1
Substituting the values of δ2 and δ1:
Ratio = (W*L^3)/(3EI) / (WL^3)/(3EI)
The E, I, and b values cancel out in the numerator and denominator, so we are left with:
Ratio = (W*L^3)/(WL^3) = 1
Therefore, the ratio of deflection at the free end after doubling the length of the beam and reducing the load to half compared to the original deflection is 1.
Answer:
The deflection at the free end is the same, so the ratio is 1, which is equivalent to 4 times the original deflection. Therefore, the correct answer is option 'B' - 4 times.