Applications of integral calculus — Question 210
Original QCE Vault practice · 5 marks
Q210 · Practice questionTechnology-freeComplex familiar5 marks
QUESTION 210 (5 marks)
A decorative shade uses the region R between y=ex and y=e−x on 0≤x≤ln2. 
a)Determine the exact area.
[2 marks] b)Determine exact volume when R rotates about the x-axis.
[3 marks] WORKED SOLUTION
Practice marking scheme
5 marksANSWER(a) 1/2. (b) 9π/8. Worked solution
(a) The upper curve is exp(x). Thus A=∫0ln2(ex−e−x)dx=[ex+e−x]0ln2=2+1/2−2=1/2. (b) Use washers:
V=π∫0ln2(e2x−e−2x)dx=2π[e2x+e−2x]0ln2=2π(4+1/4−2)=9π/8. Subtract squared radii; the square of the radius difference would be incorrect.
Equivalent mathematically justified methods accepted.
Exact answers unless a decimal accuracy is specified.
Part a: Integrate upper minus lower.
[1 mark]Part a: Evaluate the area.
[1 mark]Part b: Form the difference of squared radii.
[1 mark]Part b: Integrate the exponential terms.
[1 mark]Part b: Evaluate exact volume.
[1 mark]Practice question aligned to the current QCAA syllabus; review the worked solution and marking criteria.
View the QCAA syllabusHow many marks did you earn?Compare your working with the guide above.
Related questions
- Q208 · Original practice · 8 marks
A vessel design starts with region R below y=x, above the x-axis and to the left of x=4. R is rotated about the y-axis. Applications of integral calculus - Q209 · Original practice · 5 marks
For k>0, the region below y=ksinx and above the x-axis on 0≤x≤π is rotated about the x-axis. Applications of integral calculus - Q283 · Original practice · 8 marks
A waiting time T has density f(t)=kte−2t for t≥0 and zero otherwise, with k>0. For this question you may use E(T)=∫0∞tf(t)dt,E(T2)=∫0∞t2f(t)dt,Var(T)=E(T2)−[E(T)]2. All relevant integrals converge; polynomial factors times e−2t tend to zero at infinity. Applications of integral calculus - Q296 · Original practice · 5 marks
A channel has the depths in the supplied table, measured at equally spaced positions across its 4 m width. The water has uniform downstream speed 0.75 m/s. The flow rate equals cross-sectional area times downstream speed.
Applications of integral calculus