<h3>
Answer: D) 30</h3>
Angle of incidence always equals angle of reflection. Think of a tennis ball being hit into a wall. The ball will bounce off at the same angle that it approached with. The angles mentioned are formed through the line called the "normal", which is the line perpendicular to the surface.
Momentum P is conserved because there are no external forces acting on the system.
P before = P after = m₁ v₁ + m₂ v₂
m₁ = 1
m₂ = 5
before:
v₁ = 1
v₂ = 0
Pᵇ = 1·1 + 5 · 0
after:
v₁ = v₂
Pᵃ = Pᵇ
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In series circuit, Req = R₁ + R₂ + R₃ + ···
In parallel circuit, 
<h3>Q7.</h3>
total resistance in the upper branch = R₂ + R₃ = R₂ + 2
R₂ + 2 = 12
R₂ = 10Ω
<h3>Q8.</h3>
Req = 1.7Ω
