CAIE M2 2014 June — Question 6

Exam BoardCAIE
ModuleM2 (Mechanics 2)
Year2014
SessionJune
PaperDownload PDF ↗
Mark schemeDownload PDF ↗
TopicCircular Motion 1
TypeParticle on table with string above
DifficultyModerate -0.5 This appears to be a standard circular motion problem involving a conical pendulum or particle on a table with string through a hole. These are routine M2 exercises requiring resolution of forces and application of F=mrω². The setup is typical and the solution method is well-practiced, making it easier than average but not trivial.
Spec6.06a Variable force: dv/dt or v*dv/dx methods

6 A particle \(P\) of mass 0.6 kg is released from rest at a point above ground level and falls vertically. The motion of \(P\) is opposed by a force of magnitude \(3 v \mathrm {~N}\), where \(v \mathrm {~m} \mathrm {~s} ^ { - 1 }\) is the speed of \(P\). Immediately before \(P\) reaches the ground, \(v = 1.95\).
  1. Calculate the time after its release when \(P\) reaches the ground. \(P\) is now projected horizontally with speed \(1.95 \mathrm {~m} \mathrm {~s} ^ { - 1 }\) across a smooth horizontal surface. The motion of \(P\) is again opposed by a force of magnitude \(3 v \mathrm {~N}\), where \(v \mathrm {~m} \mathrm {~s} ^ { - 1 }\) is the speed of \(P\).
  2. Calculate the distance \(P\) travels after projection before coming to rest.

Question 6:
Part (i):
AnswerMarks Guidance
WorkingMarks Guidance
\(0.6\,dv/dt = 0.6g - 3v\)B1 Newton's Second Law
\(\int 1/(10-5v)\,dv = \int dt\)M1 \(0.6\int 1/(0.6g - 3v)\,dv = \int dt\)
\(-\frac{1}{5}\ln(10 - 5v) = t(+c)\)A1 \(\frac{0.6}{-3}\ln(0.6g - 3v) = t(+c)\)
Finds \(c\) or uses limits twiceM1
\(t = 0.738 \text{ s}\)A1
Total: 5 marks
Part (ii):
AnswerMarks Guidance
WorkingMarks Guidance
\(0.6v\,dv/dx = -3v\)B1 Newton's Second Law
\(\int 0.2\,dv = -\int dx\)M1 Integration with use of limits or finding \(c\)
\(x = 0.39 \text{ m}\)A1
Total: 3 marks
## Question 6:

### Part (i):

| Working | Marks | Guidance |
|---------|-------|----------|
| $0.6\,dv/dt = 0.6g - 3v$ | B1 | Newton's Second Law |
| $\int 1/(10-5v)\,dv = \int dt$ | M1 | $0.6\int 1/(0.6g - 3v)\,dv = \int dt$ |
| $-\frac{1}{5}\ln(10 - 5v) = t(+c)$ | A1 | $\frac{0.6}{-3}\ln(0.6g - 3v) = t(+c)$ |
| Finds $c$ or uses limits twice | M1 | |
| $t = 0.738 \text{ s}$ | A1 | |

**Total: 5 marks**

### Part (ii):

| Working | Marks | Guidance |
|---------|-------|----------|
| $0.6v\,dv/dx = -3v$ | B1 | Newton's Second Law |
| $\int 0.2\,dv = -\int dx$ | M1 | Integration with use of limits or finding $c$ |
| $x = 0.39 \text{ m}$ | A1 | |

**Total: 3 marks**

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6 A particle $P$ of mass 0.6 kg is released from rest at a point above ground level and falls vertically. The motion of $P$ is opposed by a force of magnitude $3 v \mathrm {~N}$, where $v \mathrm {~m} \mathrm {~s} ^ { - 1 }$ is the speed of $P$. Immediately before $P$ reaches the ground, $v = 1.95$.\\
(i) Calculate the time after its release when $P$ reaches the ground.\\
$P$ is now projected horizontally with speed $1.95 \mathrm {~m} \mathrm {~s} ^ { - 1 }$ across a smooth horizontal surface. The motion of $P$ is again opposed by a force of magnitude $3 v \mathrm {~N}$, where $v \mathrm {~m} \mathrm {~s} ^ { - 1 }$ is the speed of $P$.\\
(ii) Calculate the distance $P$ travels after projection before coming to rest.

\hfill \mbox{\textit{CAIE M2 2014 Q6}}