AP Physics 1 / Topic
Linear Momentum
Unit 4 covers momentum and impulse, conservation of momentum in collisions and explosions, elastic versus inelastic collisions, and center of mass.
What the exam asks
- Relate impulse to momentum change and to force-time graphs
- Apply conservation of momentum to 1D and simple 2D collisions
- Classify collisions: elastic (KE conserved) versus perfectly inelastic (objects stick)
- Explain why KE is lost in inelastic collisions while momentum is not
- Locate and track the center of mass of a system
Key formulas and rules
p = mv; J = FΔt = Δp; area under F-t graph
m1v1 + m2v2 = m1v1' + m2v2' (isolated system)
m1v1 + m2v2 = (m1 + m2)v'
elastic collisions also conserve ½mv² totals
x(cm) = Σmixi / Σmi; no external force ⇒ v(cm) constant
Question bank breakdown
41
3
10 easy · 22 medium · 9 hard
Skills covered
Every question in the bank comes with a worked explanation, and most add a per-choice breakdown so you learn why each wrong answer is wrong - not just the key.
Sample question
From the free tier of the ScoreMint AP Physics 1 bank - try it, then check the answer.
A ball traveling at to the right strikes a wall and bounces back at to the left. The ball is in contact with the wall for . What is the magnitude of the average force exerted by the wall on the ball?
- A.
- B.
- C.
- D.
Show answer and explanation
Answer: C. Impulse equals the change in momentum: . Since momentum is a vector, direction matters critically. With rightward as positive: m/s and m/s. Thus m/s. The change in momentum is kg m/s (the negative sign means the impulse is to the left, which makes sense). The average force magnitude is N. The most common error is subtracting speeds () instead of accounting for the reversal of direction.
Study tip
Momentum is a vector: pick a positive direction before plugging in, and keep the sign on every velocity. Most collision errors are sign errors, not physics errors.