MCAT Physics 4

Question 1

A concave mirror has a focal length of 10 cm. An object is placed 30 cm from the mirror. Where is the image formed?

Accepted Answer

15 cm in front of the mirror

Answer

Using 1/f = 1/do + 1/di: 1/10 = 1/30 + 1/di → 1/di = 1/10 − 1/30 = 2/30, di = 15 cm in front.

Question 2

A capacitor with capacitance 4 μF is connected to a 12 V battery. What charge is stored on the capacitor?

Accepted Answer

48 μC

Answer

Q = CV = 4 × 10⁻⁶ × 12 = 48 × 10⁻⁶ C = 48 μC.

Question 3

An object of mass m traveling at velocity v collides with an identical stationary object and the two stick together. What is their combined velocity?

Accepted Answer

v/2

Answer

By conservation of momentum, mv = 2m·v_f, so v_f = v/2.

Question 4

Which of the following is true about the electric field inside a conductor in electrostatic equilibrium?

Accepted Answer

It is zero

Answer

In electrostatic equilibrium, charges redistribute to the surface, resulting in zero electric field inside the conductor.

Question 5

A sound wave in air has an intensity of 10⁻⁶ W/m². What is the sound level in decibels? (I₀ = 10⁻¹² W/m²)

Accepted Answer

60 dB

Answer

β = 10 log(I/I₀) = 10 log(10⁻⁶/10⁻¹²) = 10 log(10⁶) = 10 × 6 = 60 dB.

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