IBDP Maths SL 5.9 Kinematic problems involving displacement, velocity and acceleration AA HL Paper 2- Exam Style Questions- New Syllabus
A particle moves in a straight line, passing through a fixed point \( O \) at \( t = 0 \). Its velocity, \( v \, \text{m/s} \), at time \( t \) seconds is given by \( v(t) = 2\sin(0.5t) + 0.3t – 2 \), for \( 0 \leq t \leq 10 \).
(a) Find the smallest value of \( t \) when the particle changes direction. [2]
(b) Find the range of values of \( t \) for which the displacement of the particle is increasing. [2]
(c) Find the displacement of the particle relative to \( O \) when \( t = 10 \). [2]
▶️ Answer/Explanation
(a) [2 marks]
Particle changes direction when \( v(t) = 0 \) (M1).
\( v(t) = 2\sin(0.5t) + 0.3t – 2 = 0 \).
Numerically, \( t \approx 1.68694 \approx 1.69 \) seconds (A1). Acceleration \( a(t) = \cos(0.5t) + 0.3 > 0 \) at \( t \approx 1.69 \), confirming direction change.
(b) [2 marks]
Displacement increases when \( v(t) > 0 \) (M1).
From graph and solving \( v(t) = 0 \), zeros at \( t \approx 1.68694 \) and \( t \approx 6.11857 \).
\( v(t) > 0 \) for \( 1.68694 < t < 6.11857 \approx 1.69 < t < 6.12 \) (A1).
(c) [2 marks]
Displacement \( s(t) = \int_0^{10} v(t) \, dt = \int_0^{10} (2\sin(0.5t) + 0.3t – 2) \, dt \) (M1).
\( s(t) = -4\cos(0.5t) + 0.15t^2 – 2t + 4 \) (using \( s(0) = 0 \)).
At \( t = 10 \): \( s(10) \approx -4\cos(5) + 0.15 \cdot 100 – 20 + 4 \approx -2.13464 \approx -2.13 \, \text{m} \) (A1).
Markscheme Answers:
(a) recognition that velocity is zero (M1)
\( t = 1.68694 \ldots \approx 1.69 \) (A1)
(b) recognition that \( v > 0 \) (M1)
\( 1.68694 \ldots < t < 6.11857 \ldots \approx 1.69 < t < 6.12 \) (A1)
(c) attempt to substitute into the total displacement formula (M1)
\( \int_0^{10} (2\sin(0.5t) + 0.3t – 2) \, dt = -2.13464 \ldots \approx -2.13 \, \text{m} \) (A1)
Total [6 marks]