OCR M3 2008 January — Question 1 6 marks

Exam BoardOCR
ModuleM3 (Mechanics 3)
Year2008
SessionJanuary
Marks6
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TopicImpulse and momentum (advanced)
TypeVelocity after impulse (direct calculation)
DifficultyModerate -0.8 This is a straightforward application of the impulse-momentum theorem in 2D. Part (i) requires basic vector addition (initial momentum + impulse = final momentum) and Pythagoras for speed. Part (ii) simply requires recognizing that if motion is parallel to x-axis, the y-component of velocity must be zero, so the impulse must cancel the existing y-momentum. No problem-solving insight needed, just routine application of standard formulas.
Spec6.03f Impulse-momentum: relation6.03g Impulse in 2D: vector form

1 A smooth horizontal surface lies in the \(x - y\) plane. A particle \(P\) of mass 0.5 kg is moving on the surface with speed \(5 \mathrm {~m} \mathrm {~s} ^ { - 1 }\) in the \(x\)-direction when it is struck by a horizontal blow whose impulse has components - 3.5 N s and 2.4 N s in the \(x\)-direction and \(y\)-direction respectively.
  1. Find the components in the \(x\)-direction and the \(y\)-direction of the velocity of \(P\) immediately after the blow. Hence show that the speed of \(P\) immediately after the blow is \(5.2 \mathrm {~m} \mathrm {~s} ^ { - 1 }\). \(P\) is struck by a second horizontal blow whose impulse is \(\mathbf { I }\).
  2. Given that \(P\) 's direction of motion immediately after this blow is parallel to the \(x\)-axis, write down the component of \(\mathbf { I }\) in the \(y\)-direction.

1 A smooth horizontal surface lies in the $x - y$ plane. A particle $P$ of mass 0.5 kg is moving on the surface with speed $5 \mathrm {~m} \mathrm {~s} ^ { - 1 }$ in the $x$-direction when it is struck by a horizontal blow whose impulse has components - 3.5 N s and 2.4 N s in the $x$-direction and $y$-direction respectively.\\
(i) Find the components in the $x$-direction and the $y$-direction of the velocity of $P$ immediately after the blow. Hence show that the speed of $P$ immediately after the blow is $5.2 \mathrm {~m} \mathrm {~s} ^ { - 1 }$.\\
$P$ is struck by a second horizontal blow whose impulse is $\mathbf { I }$.\\
(ii) Given that $P$ 's direction of motion immediately after this blow is parallel to the $x$-axis, write down the component of $\mathbf { I }$ in the $y$-direction.

\hfill \mbox{\textit{OCR M3 2008 Q1 [6]}}