The Student Room Group

P3 Questions

1) y = x(sinx)^0.5, 0 < x < pi. The maximum point on the curve is A.

a) Show that the x-coordinate of the point A satisfies the equation 2tanx+x=0.

The finite region enclosed by the curve and the x-axis is shaded as shown in Fig. 1 (It's in the book, so I can't show it. Sorry.).

A solid body S is generated by rotating this region through 2pi radians about the x-axis.

b) Find the exact volume of S.

2) Relative to a fixed origin O, the point A has position vector 3i+2j-k, the point B has position vector 5i+j+k, and the point C has position vector 7i-j.

a) Find the cosine of angle ABC.

b) Find the exact value of the area of the triangle ABC.

The point D has position vector 7i+3k.

c) Show that AC is perpendicular to CD.

d) Find the ratio AD:biggrin:B.

3) Fluid flows out of a cylindrical tank with constant cross section. At time t minutes, t is greater than or equal to 0, the volume of fluid remaining in the tank is Vm^3. The rate at which the fluid flows, in m^3 min^-1, is proportional to the square root of V.

a) Show that the depth h metres of fluid in the tank satisfies the differential equation

dh/dt = -k&#8730;h, where k is a positive constant.

b) Show that the general solution of the differential equation may be written as

h = (A-Bt)^2, where A and B are constants.

Given that at time t=0, the depth of fluid in the tank is 1m, and that 5 minutes later, the depth of fluid has reduced to 0.5m.

c) Find the time, T minutes, which it takes for the tank to empty.

d) Find the depth of water in the tank at time 0.5T minutes.

4) f(x) = 25/(1-x)(3+2x)^2, |x|=1.

a) Express f(x) as a sum of partial fractions.

b) Hence find the integral of f(x) dx.

c) Find the series expansion of f(x) in ascending powers of x up to and including the term in x^2. Give each coefficient as a simplified fraction.

Answers:

1b) pi[pi^2-4].
2a) -4/9.
2b) 0.5&#8730;65.
2d) 2:-1.
3c) 17.1 min.
3d) 0.25m
8b) -ln|1-x| + ln|2x+3| - (2x-8)(2x+3)^-1 + C.
8c) 25/9 - 25x/27 + 25x^2/9...

Cheers :smile:
Aristotle
1) y = x(sinx)^0.5, 0 < x < pi. The maximum point on the curve is A.

a) Show that the x-coordinate of the point A satisfies the equation 2tanx+x=0.

The finite region enclosed by the curve and the x-axis is shaded as shown in Fig. 1 (It's in the book, so I can't show it. Sorry.).

A solid body S is generated by rotating this region through 2pi radians about the x-axis.

b) Find the exact volume of S.

1

a)

y = x(sinx)^½
dy/dx = x(½ cosx)(sinx)^-½ + (sinx)^½

turning point at dy/dx = 0

0 = (x/2)cosx(sinx)^-½ + (sinx)^½
-(sinx)^½ = [x/2(cosx)]/(sinx)^½
-2sinx = xcosx
-2tanx = x
0 = x + 2tanx
1

b) (integration by parts, twice)
V = pi &#8747; dx
V = pi &#8747;x²sinx dx

u =x² ; v' = sinx
u' = 2x ; v =-cosx
&#8747; uv' = uv - &#8747;u'v
&#8747; x²sinx dx = x².(-cosx) - &#8747; -2xcosx dx
&#8747; x²sinx dx = x².(-cosx) + 2 &#8747; xcosx dx


&#8747; xcosx dx
let u=x ; v'=cosx
u' =1 ; v=sinx
&#8747; xcosx dx = xsinx -&#8747; sinx dx
&#8747; xcosx dx = xsinx + cosx


V = pi &#8747;x²sinx dx
V = pi {-x²cosx + 2[xsinx + cosx] }

limits are pi to 0.

V = pi (pi^2 -4)