AP Physics 1 — Unit 2: Force and Translational Dynamics
Practice questions, answers, and key terms for Unit 2, aligned to the College Board CED.
AP Physics 1 Unit 2 practice questions
Two pucks sit on a frictionless table: 2 kg at x = 0 and 4 kg at x = 3 m. Where is the center of mass of the system?
x_cm = 2 m, from (2·0 + 4·3)/6 = 12/6. It sits closer to the heavier puck.
A diver curls into a tight ball mid-flip, then extends. Internal muscle forces are firing the whole time. What happens to the path of her center of mass?
Her center of mass follows the same parabolic projectile path the whole time. Internal forces can rearrange her body but cannot change the motion of the system's center of mass.
You can treat a rolling bowling ball as a single point at its center, but you can't treat a folding ladder being opened that way. What's the deciding factor?
Only when the internal structure doesn't affect the behavior. A single-point model breaks when internal rearrangement, like opening the ladder, changes shape.
A student draws a free-body diagram of a book resting on a table and adds an arrow labeled 'force of motion' pointing the way the book was last slid. What's wrong?
There is no 'force of motion' — only gravity and the normal force act. A free-body diagram shows present forces; past motion exerts none.
Your lab partner insists a thrown ball mid-flight has an upward 'force from the hand' keeping it going. The ball already left the hand. What forces actually act on it?
Only gravity (ignoring air resistance). Once the ball leaves the hand, the hand no longer touches it, so it can exert no force. The ball coasts upward on inertia, not a stored force.
A crate sits on a ramp inclined at angle θ. To set up the free-body diagram, why is it smart to tilt your coordinate axes so one axis runs along the ramp surface?
It puts the acceleration on a single axis along the ramp. Then only gravity has to be split into components.
On a free-body diagram of a hanging lamp, a student draws the gravity arrow starting at the ceiling hook and another arrow showing the lamp pulling on the cord. Two mistakes — what are they?
Two mistakes: arrows must start at the dot, and only forces ON the lamp belong. The lamp's pull on the cord goes on the cord's diagram.
A horse pulls a cart and the cart pulls back on the horse with an equal and opposite force (Newton's 3rd law). If the forces are equal, how does the system ever accelerate forward?
The action-reaction pair acts on two DIFFERENT objects, so they never cancel. The cart accelerates from the net force on it: pull minus friction.
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Key terms in Unit 2
These 12 terms show up in the Unit 2 cards. Each one links to its definition in the AP Physics 1 key-term reference.
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