2005 Paper 2 Q11

Year: 2005
Paper: 2
Question Number: 11

Course: LFM Pure and Mechanics
Section: Pulley systems

Difficulty: 1600.0 Banger: 1502.0

Problem

A plane is inclined at an angle \(\arctan \frac34\) to the horizontal and a small, smooth, light pulley~\(P\) is fixed to the top of the plane. A string, \(APB\), passes over the pulley. A particle of mass~\(m_1\) is attached to the string at \(A\) and rests on the inclined plane with \(AP\) parallel to a line of greatest slope in the plane. A particle of mass \(m_2\), where \(m_2>m_1\), is attached to the string at \(B\) and hangs freely with \(BP\) vertical. The coefficient of friction between the particle at \(A\) and the plane is \( \frac{1}{2}\). The system is released from rest with the string taut. Show that the acceleration of the particles is \(\ds \frac{m_2-m_1}{m_2+m_1}g\). At a time \(T\) after release, the string breaks. Given that the particle at \(A\) does not reach the pulley at any point in its motion, find an expression in terms of \(T\) for the time after release at which the particle at \(A\) reaches its maximum height. It is found that, regardless of when the string broke, this time is equal to the time taken by the particle at \(A\) to descend from its point of maximum height to the point at which it was released. Find the ratio \(m_1 : m_2\). \noindent [Note that \(\arctan \frac34\) is another notation for \(\tan^{-1} \frac34\,\).]

No solution available for this problem.

Rating Information

Difficulty Rating: 1600.0

Difficulty Comparisons: 0

Banger Rating: 1502.0

Banger Comparisons: 2

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Problem source
A plane is   inclined at an 
angle $\arctan \frac34$ to the horizontal and 
 a small, smooth, light pulley~$P$ 
is fixed to the top of the  plane.  A string, $APB$, passes over the pulley.
A particle  of mass~$m_1$ 
is attached to  the string at $A$ and rests on the inclined plane with $AP$ 
parallel to a line of greatest slope in the plane. 
A particle of mass $m_2$, where $m_2>m_1$,
 is attached to the string at $B$ 
and hangs freely with $BP$ 
vertical. The coefficient of 
friction between the particle at $A$ 
and the plane is $ \frac{1}{2}$.  
 
The system is released from rest with the string taut. 
Show that the acceleration of the 
particles is $\ds \frac{m_2-m_1}{m_2+m_1}g$. 
 
At a time $T$ after release, the string breaks.
Given that the particle at $A$
does not reach the pulley at any point in its motion,
find an expression  in terms of $T$ for the time 
after release at which the particle at $A$ 
reaches its maximum height. It is found that, regardless 
of when the string broke, this time is equal to the time 
taken by the particle at $A$  to descend 
from its point of maximum height to the point 
at which it was released. Find the ratio $m_1 : m_2$.  
\noindent
[Note that $\arctan \frac34$ is another notation for $\tan^{-1} \frac34\,$.]