Small smooth spheres $$\(A\)$$ and $$\(B\)$$, of equal radii and of masses $$\(4 \mathrm{~kg}\)$$ and $$\(2 \mathrm{~kg}\)$$ respectively, lie on a smooth horizontal plane. Initially $$\(B\)$$ is at rest and $$\(A\)$$ is moving towards $$\(B\)$$ with speed $$\(10 \mathrm{~m} \mathrm{~s}^{-1}\)$$. After the spheres collide $$\(A\)$$ continues to move in the same direction but with half the speed of $$\(B\)$$. A third small smooth sphere $$\(C\)$$, of mass $$\(1 \mathrm{~kg}\)$$ and with the same radius as $$\(A\)$$ and $$\(B\)$$, is at rest on the plane. $$\(B\)$$ now collides directly with $$\(C\)$$. After this collision $$\(B\)$$ continues to move in the same direction but with one third the speed of $$\(C\)$$. $$\(A\)$$ and $$\(B\)$$ coalesce during this collision. Find the total loss of kinetic energy in the system due to the three collisions. ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................
Exam No:9709_s20_qp_42 Year:2020 Question No:4(c)
Answer:
Conservation of momentum \(A, B\)
\(4 \times\) their \(5+2 \times\) their \(4=4 v+2 v \quad v=\frac{14}{3}\left(\mathrm{~ms}^{-1}\right)\)
\(\mathrm{KE}\) initial \(=\frac{1}{2} \times 4 \times 10^{2}\)
\(\mathrm{KE}\) final \(=\frac{1}{2} \times 6 \times\) their \(\left(\frac{14}{3}\right)^{2}+\frac{1}{2} \times 1 \times\) their \(12^{2}\)
Loss of \(\mathrm{KE}=200-\frac{412}{3}=\frac{188}{3}\)
\(4 \times\) their \(5+2 \times\) their \(4=4 v+2 v \quad v=\frac{14}{3}\left(\mathrm{~ms}^{-1}\right)\)
\(\mathrm{KE}\) initial \(=\frac{1}{2} \times 4 \times 10^{2}\)
\(\mathrm{KE}\) final \(=\frac{1}{2} \times 6 \times\) their \(\left(\frac{14}{3}\right)^{2}+\frac{1}{2} \times 1 \times\) their \(12^{2}\)
Loss of \(\mathrm{KE}=200-\frac{412}{3}=\frac{188}{3}\)
Knowledge points:
4.5.2 understand the concepts of gravitational potential energy and kinetic energy, and use appropriate formulae
Solution:
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