Figure 4 shows two particles P and Q of mass 3 kg and 2 kg respectively, connected by a light inextensible string - Edexcel - A-Level Maths Mechanics - Question 7 - 2007 - Paper 1
Question 7
Figure 4 shows two particles P and Q of mass 3 kg and 2 kg respectively, connected by a light inextensible string. Initially P is held at rest on a fixed smooth plan... show full transcript
Worked Solution & Example Answer:Figure 4 shows two particles P and Q of mass 3 kg and 2 kg respectively, connected by a light inextensible string - Edexcel - A-Level Maths Mechanics - Question 7 - 2007 - Paper 1
Step 1
Write down an equation of motion for P and an equation of motion for Q.
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Answer
For particle Q (2 kg):
2g−T=2a
For particle P (3 kg):
T−3gextsin(30exto)=3a
Step 2
Hence show that the acceleration of Q is 0.98 m s⁻².
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Answer
From the equations derived, we can set them equal to find the acceleration:
Substituting the known values:
2g−T=2aextandT−3gextsin(30exto)=3a
We find that the acceleration of Q is 0.98 m s⁻².
Step 3
Find the tension in the string.
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Answer
To find the tension, we can rewrite one of the equations:
Using the first equation: T=2g−2a
Substituting the values gives us:
Textapproximately18N
Step 4
State where in your calculations you have used the information that the string is inextensible.
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Answer
I used the fact that the string is inextensible to equate the magnitudes of the accelerations of both P and Q. This means both particles must experience the same magnitude of acceleration when the system is released.
Step 5
the speed of Q as it reaches the ground.
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Answer
Using the equation of motion:
v2=u2+2as
With initial speed u=0, the total distance s=0.8extm and a=0.98extms−2, we find:
v=extapproximately1.568extms−1
Step 6
the time between the instant when Q reaches the ground and the instant when the string becomes taut again.
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Answer
Using the equation:
s = ut + rac{1}{2}at^2
Where u=0, s=0.8 m, and a=0.98 m/s².
Solving for t gives: textapproximately0.5exts