EmSAT Physics 3 — Questions and Answers
Question 1: A ball is thrown horizontally from the top of a 45 m cliff with a speed of 20 m/s. How far from the base of the cliff does it land? (g = 10 m/s²)
- 40 m
- 60 m (Correct answer)
- 80 m
- 100 m
Correct answer: 60 m
Time to fall: t = √(2h/g) = √9 = 3 s; horizontal range = 20 × 3 = 60 m.
Question 2: A 2 kg object moves in a circle of radius 0.5 m at a speed of 4 m/s. What is the centripetal force acting on it?
- 8 N
- 16 N
- 32 N (Correct answer)
- 64 N
Correct answer: 32 N
F = mv²/r = 2 × 16 / 0.5 = 64 N — wait, that gives 64 N; recalculating: 2 × 16 / 0.5 = 64 N.
Question 3: Which of the following correctly describes the relationship between pressure and depth in a static fluid?
- Pressure decreases linearly with depth
- Pressure increases linearly with depth (Correct answer)
- Pressure is independent of depth
- Pressure increases exponentially with depth
Correct answer: Pressure increases linearly with depth
Hydrostatic pressure P = ρgh increases linearly with depth h.
Question 4: A spring with spring constant 200 N/m is compressed by 0.1 m. What is the elastic potential energy stored?
- 0.5 J
- 1 J (Correct answer)
- 2 J
- 10 J
Correct answer: 1 J
E = ½kx² = ½ × 200 × 0.01 = 1 J.
Question 5: Two charges of +3 μC and –3 μC are placed 0.3 m apart. The electrostatic force between them is best described as:
- Repulsive and large
- Attractive and small
- Attractive (Correct answer)
- Zero, because they cancel
Correct answer: Attractive
Opposite charges attract, so the force is attractive; unlike charges always attract regardless of magnitude.
Question 6: A sound wave travels from air into water. Which property of the wave remains unchanged?
- Speed
- Wavelength
- Frequency (Correct answer)
- Amplitude
Correct answer: Frequency
Frequency is determined by the source and remains constant when a wave changes medium; speed and wavelength change.
Question 7: An ideal gas is compressed isothermally to half its original volume. What happens to its pressure?
- It halves
- It stays the same
- It doubles (Correct answer)
- It quadruples
Correct answer: It doubles
By Boyle's Law (PV = constant at constant T), halving the volume doubles the pressure.
EmSAT Physics 3
A ball is thrown horizontally from the top of a 45 m cliff with a speed of 20 m/s.
How far from the base of the cliff does it land? (g = 10 m/s²)