Chemegate

GATE 2024 Chemical Engineering, Q51 · Mathematics

The correct answer is 4.91 to 4.95.

Question

Consider the line integral ∫C\int _{C} F(r)·dr, with F(r) = x î + y ĵ + z k̂, where î, ĵ and k̂ are unit vectors in the (x,y,z) Cartesian coordinate system. The path C is given by r(t) = cos(t) î + sin(t) ĵ + t k̂, where 0≤0 \leq t ≤π.\leq π. The value of the integral, rounded off to 2 decimal places, is _________

Official answer: 4.91 to 4.95

Why

GATE 2024 official key: 4.91 to 4.95. F·dr =d[½(x2+y2+z2)],= d[½(x²+y²+z²)], a conservative field, so the integral =½[(x2+y2+z2)]0π=½[(1+π2)−1]=π2/2≈4.93.= ½[(x²+y²+z²)]₀^{π} = ½[(1+π²)−1] = π²/2 \approx 4.93.

Explanation cross-checked for consistency. Final answer matches the official IIT answer key.