An object weighing 420 N in air is immersed in water after being tied to a string connected to a bal

JAMB Physics 2023 64 views

An object weighing 420 N in air is immersed in water after being tied to a string connected to a balance. The scale now reads 380 N. Find the density of the object [density of water = 1.00 x 103 kgm-3, g = 9.8 ms-2]

An object weighing 420 N in air is immersed in water after being tied to a string connected to a balance. The scale now reads 380 N. Find the density of the object [density of water = 1.00 x 103 kgm-3, g = 9.8 ms-2]

  1. 1.05 x 104 kgm-3 ✓
  2. 1.50 x 104 kgm-3
  3. 1.05 x 103 kgm-3
  4. 1.50 x 103 kgm-3

Explanation

Energy stored in capacitor: E = ½CV² = ½QV = ½Q²/C. Energy is stored in the electric field between the plates, not in the charges themselves.

Capacitors in series: 1/C_total = 1/C₁ + 1/C₂ (total less than smallest). In parallel: C_total = C₁ + C₂ (total equals sum). Opposite rules to resistors.

Charging curve is exponential. Time constant τ = RC (time to reach 63% of final charge). After 5τ, capacitor is essentially fully charged.

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