AP Physics Physics: Classical Mechanics & Kinematics 4 — Questions and Answers
Question 1: A satellite orbits Earth at constant speed in a circular orbit. Which statement correctly describes its motion?
- It is in equilibrium with zero net force
- Gravity provides centripetal force toward Earth's center (Correct answer)
- Its acceleration is zero because speed is constant
- Gravity and inertia cancel, producing no net force
Correct answer: Gravity provides centripetal force toward Earth's center
Gravity acts as centripetal force pulling the satellite toward Earth's center, causing circular orbital motion.
Question 2: On an Atwood machine, masses of 3 kg and 5 kg are connected by a massless string over a frictionless pulley. What is the system's acceleration? (g = 10 m/s²)
- 1.25 m/s²
- 2.5 m/s² (Correct answer)
- 5 m/s²
- 10 m/s²
Correct answer: 2.5 m/s²
For an Atwood machine, a = (m₂−m₁)g/(m₁+m₂) = (5−3)(10)/(3+5) = 20/8 = 2.5 m/s².
Question 3: A position-time graph shows a straight line with a negative slope passing through the origin. What does this indicate?
- The object is accelerating in the positive direction
- The object moves at constant velocity in the negative direction (Correct answer)
- The object is decelerating and coming to rest
- The object is stationary
Correct answer: The object moves at constant velocity in the negative direction
A straight line on a position-time graph means constant velocity; a negative slope means the object moves in the negative direction.
Question 4: A 2 kg object is dropped from rest and falls for 3 s. Neglecting air resistance, what is its speed just before impact? (g = 10 m/s²)
- 10 m/s
- 20 m/s
- 30 m/s (Correct answer)
- 45 m/s
Correct answer: 30 m/s
Using v = v₀ + at = 0 + 10(3) = 30 m/s.
Question 5: An object travels in a straight line with increasing speed in the positive direction. Which combination correctly describes its velocity and acceleration?
- v > 0, a < 0
- v < 0, a > 0
- v > 0, a > 0 (Correct answer)
- v < 0, a < 0
Correct answer: v > 0, a > 0
Increasing speed in the positive direction means both velocity and acceleration are positive.
Question 6: Two forces of 6 N and 8 N act perpendicular to each other on an object. What is the magnitude of the resultant force?
- 7 N
- 10 N (Correct answer)
- 14 N
- 48 N
Correct answer: 10 N
For perpendicular forces, F_net = √(6² + 8²) = √(36 + 64) = √100 = 10 N.
Question 7: A velocity-time graph shows a horizontal line at v = 5 m/s. Which is true?
- The object is accelerating at 5 m/s²
- The object is at rest
- The object moves at constant velocity with zero acceleration (Correct answer)
- The object is decelerating
Correct answer: The object moves at constant velocity with zero acceleration
A horizontal line on a velocity-time graph means constant velocity; slope (acceleration) is zero.
AP Physics Physics: Classical Mechanics & Kinematics 4
A satellite orbits Earth at constant speed in a circular orbit.
Which statement correctly describes its motion?