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in Physics
What is the pH of pure water at 25°C?
Explanation:
Pure water at 25°C has a pH of 7, which is neutral. This is because [H⁺] = [OH⁻] = 10⁻⁷ M, making pH = -log(10⁻⁷) = 7.
A car moving at 72 km/h applies brakes and comes to rest in 8 seconds. What is the deceleration?
A2.5 m/s²
B2.0 m/s²
C1.5 m/s²
D3.0 m/s²
Correct Answer:
A. 2.5 m/s²Explanation:
First convert 72 km/h = 20 m/s. Using v = u + at: 0 = 20 + a(8), so a = -20/8 = -2.5 m/s². Magnitude of deceleration is 2.5 m/s².
Which of the following elements has an electronic configuration of 2, 8, 7?
AChlorine
BBromine
CFluorine
DIodine
Correct Answer:
A. ChlorineExplanation:
Chlorine (Cl) has atomic number 17, with electronic configuration 2, 8, 7 (K-shell: 2, L-shell: 8, M-shell: 7).
The refractive index of a medium is 1.5. What is the speed of light in that medium? (c = 3 × 10⁸ m/s)
A1.5 × 10⁸ m/s
B2 × 10⁸ m/s
C2.5 × 10⁸ m/s
D3 × 10⁸ m/s
Correct Answer:
B. 2 × 10⁸ m/sExplanation:
Refractive index n = c/v. Therefore, v = c/n = (3 × 10⁸)/1.5 = 2 × 10⁸ m/s.
A spring with spring constant k = 100 N/m is compressed by 0.2 m. What is the elastic potential energy stored?
Explanation:
Elastic potential energy U = ½kx². U = ½ × 100 × (0.2)² = 50 × 0.04 = 2 J.
Which hormone is responsible for regulating blood glucose levels?
AAdrenaline
BInsulin
CThyroxine
DCortisol
Correct Answer:
B. InsulinExplanation:
Insulin, produced by the pancreas, lowers blood glucose by facilitating glucose uptake into cells. Glucagon raises blood glucose levels.
A 5 kg object is lifted vertically at constant velocity. What is the work done by gravity? (Height = 10 m, g = 10 m/s²)
A-500 J
B500 J
C0 J
D100 J
Correct Answer:
A. -500 JExplanation:
Work by gravity W = -mgh (negative because displacement is opposite to force direction). W = -5 × 10 × 10 = -500 J.
What is the equivalent resistance when three resistors of 6Ω, 3Ω, and 2Ω are connected in parallel?
Explanation:
For parallel connection: 1/R = 1/6 + 1/3 + 1/2 = 1/6 + 2/6 + 3/6 = 6/6 = 1. Therefore R = 1Ω.
The phenomenon where a material exhibits permanent magnetic properties is called:
AParamagnetism
BDiamagnetism
CFerromagnetism
DAntiferromagnetism
Correct Answer:
C. FerromagnetismExplanation:
Ferromagnetism is the property of materials like iron, cobalt, and nickel to retain permanent magnetic properties due to aligned electron spins.
A projectile is launched at an angle of 45° with initial velocity 20 m/s. What is the maximum height reached? (g = 10 m/s²)
Explanation:
Vertical component of velocity: u_y = 20 sin(45°) = 20/√2 = 10√2 m/s. Maximum height h = u_y²/(2g) = (10√2)²/(2×10) = 200/20 = 10 m.
