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Solve $$\frac{3x}{x-2} \leq 1$$ An aircraft flying horizontally at $V \; \text{m s}^{-1}$ releases a bomb that hits the ground 4000 m away, measured horizontally - HSC - SSCE Mathematics Extension 1 - Question 4 - 2001 - Paper 1

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Solve-$$\frac{3x}{x-2}-\leq-1$$--An-aircraft-flying-horizontally-at-$V-\;-\text{m-s}^{-1}$-releases-a-bomb-that-hits-the-ground-4000-m-away,-measured-horizontally-HSC-SSCE Mathematics Extension 1-Question 4-2001-Paper 1.png

Solve $$\frac{3x}{x-2} \leq 1$$ An aircraft flying horizontally at $V \; \text{m s}^{-1}$ releases a bomb that hits the ground 4000 m away, measured horizontally. T... show full transcript

Worked Solution & Example Answer:Solve $$\frac{3x}{x-2} \leq 1$$ An aircraft flying horizontally at $V \; \text{m s}^{-1}$ releases a bomb that hits the ground 4000 m away, measured horizontally - HSC - SSCE Mathematics Extension 1 - Question 4 - 2001 - Paper 1

Step 1

Solve $$\frac{3x}{x-2} \leq 1$$

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Answer

To solve the inequality, we first rearrange it: 3xx210.\frac{3x}{x-2} - 1 \leq 0. This simplifies to: 3x(x2)x202x+2x202(x+1)x20.\frac{3x - (x-2)}{x-2} \leq 0 \\ \Rightarrow \frac{2x + 2}{x-2} \leq 0 \\ \Rightarrow \frac{2(x+1)}{x-2} \leq 0. Next, we find the critical points by setting the numerator and denominator to zero:

  • The numerator gives us x=1x = -1
  • The denominator gives us x=2x = 2.
    We then test the intervals formed by these critical points:
  • For x<1x < -1: Pick x=22(2+1)22=24=12>0x = -2 \Rightarrow \frac{2(-2 + 1)}{-2 - 2} = \frac{-2}{-4} = \frac{1}{2} > 0
  • For 1<x<2-1 < x < 2: Pick x=02(0+1)02=22=1<0x = 0 \Rightarrow \frac{2(0 + 1)}{0 - 2} = \frac{2}{-2} = -1 < 0
  • For x>2x > 2: Pick x=32(3+1)32=81>0x = 3 \Rightarrow \frac{2(3 + 1)}{3 - 2} = \frac{8}{1} > 0.
    Therefore, the solution is: [1,2)[-1, 2).

Step 2

Find the speed $V$ of the aircraft.

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Answer

From the problem:

  • The horizontal distance is given as x=4000mx = 4000 m,
  • The relationship between xx and tt is given by: x=Vtx = Vt So, V=xtV = \frac{x}{t}.

The vertical distance can also be expressed: From the equation for yy, y=5t2.y = -5t^2.
At the moment before impact, when y=0y = 0, we set: 0=5t2t=0=0not valid, we look for the time when it hits the ground. Note for 45 degrees: tan(45)=1yxy=x.0 = -5t^2 \Rightarrow t = \sqrt{0} = 0 \\ \Rightarrow \text{not valid, we look for the time when it hits the ground. Note for 45 degrees: } \tan(45^{\circ}) = 1 \Rightarrow \frac{y}{x} \Rightarrow y = x.
Given that the bomb hits the ground 4000m4000 m horizontally away at 4545^{\circ}, the equations of projectile motion apply. We need to find the time taken to drop this vertical distance from the height hh: Substituting back, we can find the exact numbers for motion to calculate VV. Resolving the values, we consider:

  • For yy to be similar in coordinate system, it means solving specifically for time taken at the respective coordinates which solves within given conditions, thus x=4000x = 4000 meets conditions at horizontal speed.

Step 3

Find $x$ as a function of $t$ if $$\frac{dx}{dt} = -4x$$

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Answer

We can solve this first-order differential equation using separation of variables. dxx=4dt.\frac{dx}{x} = -4dt. Integrating both sides: lnx=4t+C,\ln|x| = -4t + C, where CC is the constant of integration. Exponentiating both sides: x=e4t+C=ke4t,x = e^{-4t + C} = ke^{-4t}, where k=eCk = e^C is a constant.

To find kk, we use the initial conditions provided at time t=0t=0. Given x=3x = 3, Therefore: 3=ke0,k=3.3 = ke^{0}, \Rightarrow k = 3. Hence, we have: x=3e4t.x = 3e^{-4t}. Considering further condition of x=6/3x = -6/3, solving the constant conditions again provides:
In similarly derived cases for harmonic system of xx gives out final conditions for specific resonation values at completing oscillation motion.

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