Physics Flashcards

A car decelerates uniformly from 30 m/s to rest over a distance of 90 m. What is the magnitude of the deceleration?

Answer: 5 m/s²

Using v² = u² – 2as: 0 = 900 – 2a(90) → a = 900/180 = 5 m/s².

According to the law of conservation of momentum, when two objects collide and stick together, the total momentum:

Answer: Is conserved

In any collision with no external forces, total momentum before equals total momentum after (conservation of momentum).

The efficiency of a machine is 80%. If the input power is 500 W, what is the useful output power?

Answer: 400 W

Output power = efficiency × input power = 0.80 × 500 = 400 W.

Which process transfers heat without requiring a medium?

Answer: Radiation

Radiation transfers energy via electromagnetic waves and can travel through a vacuum, unlike conduction or convection.

A photon has an energy of 3 eV. What is its approximate frequency? (h = 4.14 × 10⁻¹⁵ eV·s)

Answer: 7.25 × 10¹⁴ Hz

f = E/h = 3 / (4.14 × 10⁻¹⁵) ≈ 7.25 × 10¹⁴ Hz, which falls in the visible light range.

In Young's double-slit experiment, increasing the separation between the two slits will:

Answer: Decrease fringe spacing

Fringe spacing β = λD/d; increasing slit separation d decreases the fringe spacing.

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?

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.