A canon shell fired breaks into two equal parts at its highest point. If one part retraces the path to the…

A canon shell fired breaks into two equal parts at its highest point. If one part retraces the path to the canon with kinetic energy $E_1$ and kinetic energy of the second part is $E_2$, then
  1. $E_2=15 E_1$
  2. $E_2=E_1$
  3. $E_2=4 E_1$
  4. $E_2=9 E_1$

Solution


Momentum before explosion $ =u \cos \theta \times 2 \mathrm{~m} $ Momentum after explosion $ =-m u \cos \theta+m v_2 $ Momentum is conserved, so $ \begin{aligned} & 2 m u \cos \theta=-m u \cos \theta+m v_2 \\ & \Rightarrow \quad v_2=3 u \cos \theta \end{aligned} $ Kinetic energy of first part $ \begin{aligned} & =E_1=\frac{1}{2} m v_1^2=\frac{1}{2} m(-u \cos \theta)^2 \\ \Rightarrow \quad E_1 & =\frac{1}{2} m u^2 \cos ^2 \theta \end{aligned} $ Now, kinetic energy of second part $ =E_2=\frac{1}{2} m v_2^2=9 \times \frac{1}{2} m u^2 \cos ^2 \theta=9 E_1 $ So, $\quad E_2=9 E_1$

Asked in: AP EAMCET 2018 (22 Apr Shift 2)

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