The diagram shows the front view of a rectangular block ABCEABCE, with dimensions 14 cm by 8 cm, placed on a ramp, VEVE, tilted at an acute angle of θ∘\theta^\circ and ∠VTE=90∘\angle VTE = 90^\circ. The ramp is placed on a horizontal surface ETET and dd is the perpendicular distance from BB to ETET.

  1. (a)

    Show that d=14sin⁡θ+8cos⁡θd = 14 \sin\theta + 8 \cos\theta.

  2. (b)

    Express dd in the form Rsin⁡(θ+α)R \sin(\theta + \alpha), where R>0R > 0 and 0∘≤α≤90∘0^\circ \le \alpha \le 90^\circ.

  3. (c)

    State the maximum value of dd and find the corresponding value of θ\theta.

  4. (d)

    Find the smallest value θ\theta such that d=13d = 13.

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Worked solution

4(a)

1. Identify the horizontal and vertical components of the rectangle's sides by drawing a horizontal line through C and a vertical line from B.

Let FF be the foot of the perpendicular from CC to the horizontal line ETET. Let GG be the foot of the perpendicular from BB to the horizontal line passing through CC.
The total vertical distance dd is the sum of the vertical distance from EE to CC (which is CFCF) and the vertical distance from CC to BB (which is BGBG).
d=CF+BGd = CF + BG

2. Express the vertical segments in terms of $\theta$ using trigonometry.

In the right-angled triangle CFECFE, the angle ∠CEF=θ\angle CEF = \theta (since CECE lies on the ramp VEVE which is inclined at θ\theta).
CF=CEsin⁡θ=14sin⁡θCF = CE \sin\theta = 14 \sin\theta

In the right-angled triangle BGCBGC, the angle ∠BCG=90∘−∠FCE=90∘−(90∘−θ)=θ\angle BCG = 90^\circ - \angle FCE = 90^\circ - (90^\circ - \theta) = \theta.
BG=BCcos⁡θ=8cos⁡θBG = BC \cos\theta = 8 \cos\theta

Therefore, d=CF+BG=14sin⁡θ+8cos⁡θd = CF + BG = 14 \sin\theta + 8 \cos\theta.

Answer

d=14sin⁡θ+8cos⁡θd = 14 \sin\theta + 8 \cos\theta (shown)

4(b)

1. Identify the form and expand $R \sin(\theta + \alpha)$

d=14sin⁡θ+8cos⁡θd = 14 \sin\theta + 8 \cos\theta
Rsin⁡(θ+α)=Rsin⁡θcos⁡α+Rcos⁡θsin⁡αR \sin(\theta + \alpha) = R \sin\theta \cos\alpha + R \cos\theta \sin\alpha

2. Find the value of $R$

Comparing coefficients:
Rcos⁡α=14R \cos\alpha = 14
Rsin⁡α=8R \sin\alpha = 8
R=142+82=196+64=260=265≈16.125R = \sqrt{14^2 + 8^2} = \sqrt{196 + 64} = \sqrt{260} = 2\sqrt{65} \approx 16.125

3. Find the value of $\alpha$ and write the final expression

tan⁡α=814=47\tan\alpha = \frac{8}{14} = \frac{4}{7}
α=tan⁡−1(47)≈29.744∘≈29.7∘\alpha = \tan^{-1}\left(\frac{4}{7}\right) \approx 29.744^\circ \approx 29.7^\circ (to 1 d.p.)
d=265sin⁡(θ+29.7∘)d = 2\sqrt{65} \sin(\theta + 29.7^\circ)

Answer

265sin⁡(θ+29.7∘)2 \sqrt{65} \sin(\theta + 29.7^\circ)

4(c)

1. State the maximum value of $d$ using the $R$ value from part (b)

From part (b), d=260sin⁡(θ+29.745∘)d = \sqrt{260} \sin(\theta + 29.745^\circ).
The maximum value of sin⁡(θ+α)\sin(\theta + \alpha) is 11.
Maximum value of d=260≈16.1d = \sqrt{260} \approx 16.1 (to 3 s.f.)

2. Find the corresponding value of $\theta$

For maximum dd, sin⁡(θ+29.745∘)=1\sin(\theta + 29.745^\circ) = 1
θ+29.745∘=90∘\theta + 29.745^\circ = 90^\circ
θ=90∘−29.745∘=60.255∘≈60.3∘\theta = 90^\circ - 29.745^\circ = 60.255^\circ \approx 60.3^\circ (to 1 d.p.)

Answer

Maximum value of d=16.1d = 16.1, corresponding θ=60.3∘\theta = 60.3^\circ

4(d)

1. Set up the equation using the $R$-formula result from part (b)

From part (b), R=142+82=260R = \sqrt{14^2 + 8^2} = \sqrt{260} and tan⁡α=814  ⟹  α≈29.745∘\tan \alpha = \frac{8}{14} \implies \alpha \approx 29.745^\circ.

Equating dd to 13:
260sin⁡(θ+29.745∘)=13\sqrt{260} \sin(\theta + 29.745^\circ) = 13

2. Solve for the basic angle

sin⁡(θ+29.745∘)=13260\sin(\theta + 29.745^\circ) = \frac{13}{\sqrt{260}}
Basic angle=sin⁡−1(13260)≈53.727∘\text{Basic angle} = \sin^{-1}\left(\frac{13}{\sqrt{260}}\right) \approx 53.727^\circ

3. Find the smallest positive value of $\theta$

For the smallest value of θ\theta, we take the first quadrant solution:
θ+29.745∘=53.727∘\theta + 29.745^\circ = 53.727^\circ
θ=53.727∘−29.745∘=23.982∘≈24.0∘ (to 1 d.p.)\theta = 53.727^\circ - 29.745^\circ = 23.982^\circ \approx 24.0^\circ \text{ (to 1 d.p.)}

Answer

24.0∘24.0^\circ

AI analysis — may contain mistakes.

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