Edexcel M3 — Question 4 9 marks

Exam BoardEdexcel
ModuleM3 (Mechanics 3)
Marks9
PaperDownload PDF ↗
Mark schemeDownload PDF ↗
TopicSimple Harmonic Motion
TypeFind amplitude from speed conditions
DifficultyStandard +0.8 This M3 SHM question requires setting up and solving simultaneous equations using v² = ω²(a² - x²) for two positions, then finding the period. It involves algebraic manipulation of non-trivial equations and understanding of SHM theory beyond routine formula application, making it moderately challenging but within reach for well-prepared students.
Spec4.10f Simple harmonic motion: x'' = -omega^2 x

A particle \(P\) moves with simple harmonic motion in a straight line, with the centre of motion at the point \(O\) on the line. \(A\) and \(B\) are on opposite sides of \(O\), with \(OA = 4\) m, \(OB = 6\) m. When passing through \(A\) and \(B\), \(P\) has speed \(6\) ms\(^{-1}\) and \(4\) ms\(^{-1}\) respectively. \includegraphics{figure_4} \begin{enumerate}[label=(\alph*)] \item Find the amplitude of the motion. [6 marks] \item Show that the period of motion is \(2\pi\) s. [3 marks]
AnswerMarks Guidance
(a) \(v^2 = n^2(a^2 - x^2)\) where \(36 = n^2(a^2 - 16)\), \(16 = n^2(a^2 - 36)\)M1 A1 A1
\(36(a^2 - 36) = 16(a^2 - 16)\)
\(20a^2 = 1040\) so \(a = 7.21\) mM1 A1 A1
(b) \(n^2 = 1\) so \(n = 1\); Period \(= \frac{2\pi}{n} = 2\pi\) sM1 A1 A1 9 marks
**(a)** $v^2 = n^2(a^2 - x^2)$ where $36 = n^2(a^2 - 16)$, $16 = n^2(a^2 - 36)$ | M1 A1 A1 |
$36(a^2 - 36) = 16(a^2 - 16)$ | |
$20a^2 = 1040$ so $a = 7.21$ m | M1 A1 A1 |
**(b)** $n^2 = 1$ so $n = 1$; Period $= \frac{2\pi}{n} = 2\pi$ s | M1 A1 A1 | 9 marks
A particle $P$ moves with simple harmonic motion in a straight line, with the centre of motion at the point $O$ on the line. $A$ and $B$ are on opposite sides of $O$, with $OA = 4$ m, $OB = 6$ m.

When passing through $A$ and $B$, $P$ has speed $6$ ms$^{-1}$ and $4$ ms$^{-1}$ respectively.

\includegraphics{figure_4}

\begin{enumerate}[label=(\alph*)]
\item Find the amplitude of the motion. [6 marks]
\item Show that the period of motion is $2\pi$ s. [3 marks]
</end{enumerate}

\hfill \mbox{\textit{Edexcel M3  Q4 [9]}}