Variable Deceleration Car Stopping Analysis

00:00 10 marks

  • Exam Style - Paper 2
  • HL
  • Tier 4
  • Kinematics
  • Integration
  • Definite integrals
  • Real-world applications of calculus
  • Variable deceleration

A car traveling at an initial speed \(v_0\) begins braking. The deceleration is not constant but increases linearly with time, modeled by \(a(t) = -kt\), where \(k\) is a positive constant.

(a) Derive an expression for the velocity \(v(t)\) of the car as a function of time \(t\), given the initial velocity \(v(0) = v_0\). Then, set up a definite integral that represents the distance traveled by the car from the moment braking begins until the car comes to a complete stop. (Hint: First, find the stopping time by determining when the velocity becomes zero.)

(b) For a car with an initial speed of 30 m/s and a deceleration constant \(k = 1\;m/s^3\), calculate the stopping time and the stopping distance using the integral expression from part (a). Provide your answers with appropriate units and to three significant figures.

Part a

5 minutes 4 marks

Question

Derive the velocity function \(v(t)\) from the acceleration \(a(t)= -kt\) given \(v(0)=v_0\). Use this velocity function to determine the stopping time, and then set up the definite integral for the stopping distance, representing the distance traveled from \(t=0\) until the car stops.



Hint Hint

Hint

Integrate \(a(t)\) to find \(v(t)\). Set \(v(t) = 0\) to find the stopping time \(t_s\). The stopping distance is given by \(\int_{0}^{t_s} v(t)\,dt\).

  • Answer Answer

Complete Answer

Velocity function: \(v(t) = v_0 – \frac{k t^2}{2}\). Stopping time: \(t_s = \sqrt{\frac{2v_0}{k}}\). Stopping distance integral: \(\int_{0}^{\sqrt{2v_0/k}} \Big(v_0 – \frac{k t^2}{2}\Big)\,dt\).

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Part b

7 minutes 6 marks

Question

Using \(v_0 = 30\;m/s\) and \(k = 1\;m/s^3\), calculate the stopping time and evaluate the integral to determine the stopping distance. Give your answers to three significant figures and include units.



Hint Hint

Hint

Substitute \(v_0 = 30\) and \(k = 1\) into the expressions for stopping time and stopping distance integral from part (a). Use your GDC to evaluate the definite integral.

  • Answer Answer

Complete Answer

Stopping time \(t_s = \sqrt{60} \approx 7.75\;s\). Stopping distance \(s = 154.919… \approx 155\;m\).

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