EmSAT Physics 5 — Questions and Answers
Question 1: A car decelerates uniformly from 30 m/s to rest over a distance of 90 m. What is the magnitude of the deceleration?
- 2.5 m/s²
- 5 m/s² (Correct answer)
- 7.5 m/s²
- 10 m/s²
Correct answer: 5 m/s²
Using v² = u² – 2as: 0 = 900 – 2a(90) → a = 900/180 = 5 m/s².
Question 2: According to the law of conservation of momentum, when two objects collide and stick together, the total momentum:
- Increases
- Decreases
- Is conserved (Correct answer)
- Depends on the collision type
Correct answer: Is conserved
In any collision with no external forces, total momentum before equals total momentum after (conservation of momentum).
Question 3: The efficiency of a machine is 80%. If the input power is 500 W, what is the useful output power?
- 80 W
- 400 W (Correct answer)
- 420 W
- 625 W
Correct answer: 400 W
Output power = efficiency × input power = 0.80 × 500 = 400 W.
Question 4: Which process transfers heat without requiring a medium?
- Conduction
- Convection
- Radiation (Correct answer)
- Evaporation
Correct answer: Radiation
Radiation transfers energy via electromagnetic waves and can travel through a vacuum, unlike conduction or convection.
Question 5: A photon has an energy of 3 eV. What is its approximate frequency? (h = 4.14 × 10⁻¹⁵ eV·s)
- 3.6 × 10¹⁴ Hz
- 7.25 × 10¹⁴ Hz (Correct answer)
- 1.4 × 10¹⁵ Hz
- 3.0 × 10¹⁵ Hz
Correct answer: 7.25 × 10¹⁴ Hz
f = E/h = 3 / (4.14 × 10⁻¹⁵) ≈ 7.25 × 10¹⁴ Hz, which falls in the visible light range.
Question 6: In Young's double-slit experiment, increasing the separation between the two slits will:
- Increase fringe spacing
- Decrease fringe spacing (Correct answer)
- Have no effect on fringe spacing
- Eliminate the interference pattern
Correct answer: Decrease fringe spacing
Fringe spacing β = λD/d; increasing slit separation d decreases the fringe spacing.
Question 7: An electron makes a transition from an excited state to the ground state in a hydrogen atom. Which of the following best describes what happens?
- A photon is absorbed and the electron gains energy
- A photon is emitted and the electron loses energy (Correct answer)
- The electron's orbit radius increases
- No energy change occurs
Correct answer: A photon is emitted and the electron loses energy
When an electron drops to a lower energy level, it releases the energy difference as an emitted photon.
EmSAT Physics 5
A car decelerates uniformly from 30 m/s to rest over a distance of 90 m.
What is the magnitude of the deceleration?