Paper 2 Conservation Laws in Physics Answers

Q1 Momentum in an Explosion

1. Take right as positive. Initial momentum is zero: $0=-0.60(0.80)+0.40v_B$, so $v_B=1.2\mathrm{m}{\mathrm{s}}^{-1}$ right. [3]
2. $E_k=\frac{1}{2}(0.60)(0.80{)}^2+\frac{1}{2}(0.40)(1.2{)}^2=0.480\mathrm{J}$. [2]
3. Stored internal/elastic/chemical energy is transferred into kinetic energy while total energy is conserved. [2]

Q2 Charge Conservation at a Junction

1. Entering current $=2.4+0.70=3.10\mathrm{A}$. Leaving: $1.5+I=3.10$, so $I=1.60\mathrm{A}$. [2]
2. Conservation of charge. [1]
3. If charge accumulated, potential/current distribution would change; in steady state rate in equals rate out. [2]

Q3 Nuclear Conservation

1. Left nucleon number $=236$; right known $=141+92=233$, so $x=3$. [2]
2. Left charge $=92$; right charge $=56+36=92$, conserved. [1]
3. Product nuclei have greater total binding energy; mass decreases and energy is released by $E=\Delta m{c}^2$. [2]