Momentum

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AP Physics 1 › Momentum

Questions 1 - 10
1

A $0.50,\text{kg}$ ball moves right at $8.0,\text{m/s}$, and a $2.0,\text{kg}$ cart moves right at $1.0,\text{m/s}$. Which has the greater momentum magnitude?

They have equal momentum magnitude

The ball

The cart

The cart, because it has greater mass

Explanation

This question assesses understanding of momentum magnitude comparison in AP Physics 1. Momentum is calculated as the product of mass and velocity, with magnitude being mass times speed. Direction is part of the vector but ignored for magnitude. Here, 0.5 kg times 8 m/s is 4 kg m/s, greater than 2 kg times 1 m/s which is 2 kg m/s. A common distractor is choice D, which prioritizes mass over the mass-speed product, overlooking the faster speed of the ball. For comparisons, always multiply mass by speed and compare the results numerically.

2

A $4.0,\text{kg}$ glider moves at $+2.5,\text{m/s}$ along the $x$-axis. What is the direction of its momentum?

Negative $x$ direction

Perpendicular to the velocity

Zero, because direction is undefined for momentum

Positive $x$ direction

Explanation

This question assesses understanding of momentum direction in AP Physics 1. Momentum is a vector quantity calculated as the product of mass and velocity, sharing the same direction as the velocity vector. For motion along the x-axis, a positive velocity indicates positive x-direction for momentum. The direction is inherent to the vector nature of momentum, not perpendicular or undefined. A common distractor is choice A, which might appeal if one mistakenly reverses the sign of the given positive velocity. When determining momentum direction, always align it with the velocity vector's direction for transferable problem-solving.

3

An object moves along the $x$-axis with momentum $p=-12,\text{kg}\cdot\text{m/s}$. Which describes its motion direction?

Direction cannot be determined without mass

It moves in the negative $x$ direction

It moves in the positive $x$ direction

It is at rest

Explanation

This question assesses understanding of momentum direction from its sign in AP Physics 1. Momentum is the vector product of mass and velocity, so its sign indicates direction along an axis. A negative momentum value means motion in the negative x-direction. Mass is positive, so the sign comes solely from velocity's direction. A common distractor is choice D, which incorrectly claims direction needs mass, but mass doesn't affect direction. In one-dimensional problems, interpret the sign of p relative to your coordinate system for direction.

4

A $6.0,\text{kg}$ cart moves at $2.0,\text{m/s}$ east. A second cart has momentum magnitude $12,\text{kg}\cdot\text{m/s}$. If it moves west, what is its momentum?

$+12,\text{kg}\cdot\text{m/s}$

$+24,\text{kg}\cdot\text{m/s}$

$-24,\text{kg}\cdot\text{m/s}$

$-12,\text{kg}\cdot\text{m/s}$

Explanation

This question assesses understanding of momentum as a signed quantity in AP Physics 1. Momentum is the product of mass and velocity, with sign indicating direction (e.g., east positive, west negative). Magnitude is the absolute value, but the full momentum includes the sign. For the second cart moving west with magnitude 12, it is -12 kg m/s. A common distractor is choice A, which omits the negative sign for west direction. Assign a consistent positive direction and apply signs accordingly for vector quantities like momentum.

5

A cart of mass $5.0,\text{kg}$ moves west at $1.2,\text{m/s}$. Which is closest to its momentum $p$?

$6.0,\text{kg}\cdot\text{m/s}$ west

$3.0,\text{J}$ west

$6.0,\text{kg}\cdot\text{m/s}$ east

$3.0,\text{kg}\cdot\text{m/s}$ west

Explanation

This question assesses understanding of calculating momentum in AP Physics 1. Momentum is the product of mass and velocity, resulting in units of $ \text{kg} \cdot \text{m/s} $. It is a vector, so direction like 'west' must be included in the description. The calculation is straightforward: $5 , \text{kg}$ times $1.2 , \text{m/s}$ equals $6 , \text{kg} \cdot \text{m/s}$ west. A common distractor is choice C, which uses joules ($ \text{J} $) instead of momentum units, likely from confusing with kinetic energy. Always verify units and include direction when reporting momentum for accurate problem-solving.

6

Two carts move along a line. Cart 1: mass $3m$, speed $v$ to the left. Cart 2: mass $m$, speed $3v$ to the right. Which statement is true about momentum magnitudes?

Cart 1 has greater momentum magnitude because it is heavier

Cart 2 has greater momentum magnitude because it is faster

They have equal momentum magnitude

They have equal kinetic energy, so momentum magnitudes are equal

Explanation

This question assesses understanding of momentum magnitude with opposite directions in AP Physics 1. Momentum is the product of mass and velocity, a vector with direction matching velocity. Magnitude ignores direction, so it's mass times speed for comparison. Cart 1's 3m times v equals 3m v, same as cart 2's m times 3v. A common distractor is choice D, which confuses equal kinetic energies (both 1.5 m v²) with momentum, but they are distinct. To solve, calculate magnitudes separately and compare, regardless of direction.

7

Along one dimension, object P has mass $m$ and speed $2v$; object Q has mass $4m$ and speed $\tfrac{v}{2}$, both moving right. Which has greater momentum magnitude?

Object Q, because its kinetic energy is larger

They have equal momentum magnitude

Object Q

Object P

Explanation

This question assesses understanding of equal momentum magnitudes in AP Physics 1. Momentum is the vector product of mass and velocity, with magnitude mass times speed. Both objects move right, so directions are the same. P's m times 2v equals 2m v, matching Q's 4m times v/2. A common distractor is choice D, which mixes up momentum with kinetic energy (P has 2m v², Q has m v²). For such comparisons, focus solely on the m v product and verify calculations step-by-step.

8

Two pucks move along the same line: puck 1 has mass $m$ and speed $v$, puck 2 has mass $2m$ and speed $\tfrac{v}{3}$, both to the right. Which has greater momentum magnitude?

They have equal momentum magnitude

Puck 2

Puck 2, because it has greater kinetic energy

Puck 1

Explanation

This question assesses understanding of comparing momentum magnitudes in AP Physics 1. Momentum is defined as the product of an object's mass and its velocity, making it a vector. The magnitude is simply the scalar value of mass times speed, independent of direction. Both pucks move right, so their momenta are in the same direction, but magnitudes differ based on m v versus 2m (v/3). A common distractor is choice D, which confuses momentum with kinetic energy, as puck 2 has less momentum despite possibly different energy. For similar problems, compute m times speed for each and compare the products directly.

9

Two identical balls each have mass $m$. Ball 1 moves right at speed $v$. Ball 2 moves right at speed $2v$. How does Ball 2’s momentum compare to Ball 1’s?

Motion is along one line.

Ball 2 has four times the momentum, in the same direction.

Ball 2 has half the momentum, in the same direction.

Ball 2 has the same momentum because the masses are equal.

Ball 2 has twice the momentum, in the same direction.

Explanation

This question evaluates the relationship between speed and momentum for identical masses in AP Physics 1. Momentum is the product of mass and velocity, so for equal masses, it scales directly with velocity magnitude and shares its direction. Ball 1 has momentum m v, while Ball 2 has m times 2v, doubling the momentum in the same direction. This demonstrates how momentum depends linearly on velocity when mass is constant. Choice C distracts by confusing momentum with kinetic energy, which scales with velocity squared. A transferable strategy is to compare momenta by computing p = m v for each object and noting proportionalities.

10

A puck of mass $0.40,\text{kg}$ slides left at $3.0,\text{m/s}$ on a straight track. What is the direction of the puck’s momentum?

Take right as positive.

Left (negative $x$ direction)

Zero, because the puck is sliding on a track

Cannot be determined without the puck’s kinetic energy

Right (positive $x$ direction)

Explanation

This question assesses the understanding of momentum direction in AP Physics 1. Momentum is calculated as the product of mass and velocity, making it a vector that points in the direction of the velocity. For the puck moving left at 3.0 m/s with right as positive, its velocity is negative, so momentum is also negative, directed left. This highlights that momentum inherits the directional component from velocity, not just speed. Choice C is a distractor that wrongly assumes zero momentum due to the track, ignoring the puck's motion. A transferable strategy is to assign signs based on a chosen positive direction and compute p = m v accordingly.

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