---
title: "AP Physics 1 Unit 8 Practice Test"
description: "A timed AP Physics 1 Unit 8 (Fluids) practice test in the AP format, drawn from 1,105 multiple-choice questions and 39 FRQs written for the unit. The standard version takes about 88 minutes."
canonical: "https://fiveable.me/ap-physics-1-revised/unit-test/8"
type: "unit-test"
subject: "AP Physics 1"
unit: "Unit 8"
---

# AP Physics 1 Unit 8 Practice Test

## Overview

A timed AP Physics 1 Unit 8 (Fluids) practice test in the AP format, drawn from 1,105 multiple-choice questions and 39 FRQs written for the unit. The standard version takes about 88 minutes.

## Test Format

- 20 Multiple Choice Questions (40 minutes)
- 1 FRQ – FRQ 1 – Mathematical Routines (24 minutes)
- 1 FRQ – FRQ 2 – Translation Between Representations (24 minutes)

## Unit FRQs by Type

- [FRQ 1 – Mathematical Routines](/ap-physics-1-revised/frqs/mathematical-routines?unit=8): 13 questions
- [FRQ 2 – Translation Between Representations](/ap-physics-1-revised/frqs/translation-between-representations?unit=8): 4 questions
- [FRQ 3 – Experimental Design](/ap-physics-1-revised/frqs/experimental-design?unit=8): 5 questions
- [FRQ 4 – Qualitative/Quantitative Translation](/ap-physics-1-revised/frqs/qualitative-quantitative-translation?unit=8): 17 questions

## Practice Questions

### Question 1

A solid object of total volume V₀ and density ρ₀ floats in a liquid of density ρ_L, where ρ_L > ρ₀. Which of the following expressions gives the volume of the object that remains above the surface of the liquid?

- (A) V₀(1 - ρ₀/ρ_L)
- (B) V₀(1 - ρ_L/ρ₀)
- (C) V₀(ρ₀/ρ_L + 1)
- (D) V₀(ρ_L/ρ₀ - 1)

**Answer: (A)** Applying Archimedes' principle and volume conservation.

### Question 2

A sphere of volume V and density ρ_S is completely submerged in a liquid of density ρ_L and held stationary by a vertical string. If ρ_S > ρ_L, which of the following expressions gives the magnitude of the tension in the string?

- (A) Vg(ρ_S - ρ_L)
- (B) Vg(ρ_L - ρ_S)
- (C) Vg(ρ_S + ρ_L)
- (D) Vg(ρ_S + ρ_L)/2

**Answer: (A)** Analyzing the forces in equilibrium using Newton's second law.

### Question 3

A small object of mass m and volume V is released from rest at the bottom of a tank filled with a fluid of density ρ. The density of the object is less than ρ, and drag forces are negligible. Which expression gives the magnitude of the object's initial upward acceleration?

- (A) g(ρV/m - 1)
- (B) g(1 - ρV/m)
- (C) g(ρV/m + 1)
- (D) g(m/ρV - 1)

**Answer: (A)** Applying Newton's second law with buoyant and gravitational forces.

### Question 4

A uniform cube of side length L floats at the interface between two immiscible fluids. The top fluid has density ρ₁ and the bottom fluid has density ρ₂. If the cube is submerged such that exactly half of its volume is in each fluid, which expression gives the mass of the cube?

- (A) L³(ρ₁ + ρ₂)/2
- (B) L³(ρ₂ - ρ₁)/2
- (C) L³(ρ₁ + ρ₂)
- (D) L³(ρ₂ - ρ₁)

**Answer: (A)** Summing the buoyant forces from both displaced fluid volumes.

### Question 5

An ideal gas is enclosed in a cylinder with a movable piston. The gas initially has volume $V_0$ and density $\rho_0$. If the piston is moved to compress the gas to a new volume of $\frac{1}{3}V_0$ while keeping the mass constant, which expression represents the new density?

- (A) $3\rho_0$
- (B) $\frac{1}{3}\rho_0$
- (C) $9\rho_0$
- (D) $\frac{1}{9}\rho_0$

**Answer: (A)** Density is defined as mass per unit volume ($\rho = m/V$). Since mass is constant and volume decreases by a factor of 3, the density must increase by a factor of 3 (inverse proportionality).

### Question 6

Planet A has mass $M$ and radius $R$. Planet B has mass $4M$ and radius $2R$. If both planets are uniform spheres, which expression correctly predicts the density of Planet B ($\rho_B$) in terms of the density of Planet A ($\rho_A$)?

- (A) $\rho_B = 0.5\rho_A$
- (B) $\rho_B = 2\rho_A$
- (C) $\rho_B = 4\rho_A$
- (D) $\rho_B = 0.25\rho_A$

**Answer: (A)** Density $\rho \propto M/R^3$. For Planet B, the mass increases by factor 4 and radius by factor 2, so $\rho_B \propto 4M/(2R)^3 = 4M/8R^3 = 0.5(M/R^3)$.

### Question 7

A copper wire has length $L$, cross-sectional area $A$, and density $\rho$. The wire is stretched until its length is $2L$. Assuming the volume of the copper remains constant during stretching, what is the new density of the wire?

- (A) $\rho$
- (B) $0.5\rho$
- (C) $2\rho$
- (D) $0.25\rho$

**Answer: (A)** Density is an intensive property of the material. Since the mass and volume of the copper remain constant during the stretching process, the density does not change.

### Question 8

An ideal fluid flows through a horizontal pipe that widens from a radius of $r$ to a radius of $2r$. If the density of the fluid in the narrow section is $\rho_1$, which expression represents the fluid density $\rho_2$ in the wide section?

- (A) $\rho_2 = \rho_1$
- (B) $\rho_2 = 0.25\rho_1$
- (C) $\rho_2 = 0.5\rho_1$
- (D) $\rho_2 = 4\rho_1$

**Answer: (A)** An ideal fluid is defined as incompressible, meaning its density remains constant regardless of changes in pipe geometry or flow speed.

### Question 9

A container is filled with a volume $V$ of liquid A (density $\rho$) and a volume $V$ of liquid B (density $3\rho$). If the liquids mix completely and their volumes are additive, what is the density of the resulting mixture?

- (A) $2\rho$
- (B) $1.5\rho$
- (C) $4\rho$
- (D) $3\rho$

**Answer: (A)** Total mass is $\rho V + 3\rho V = 4\rho V$. Total volume is $2V$. The new density is total mass divided by total volume: $4\rho V / 2V = 2\rho$.

### Question 10

A chemist mixes a mass $M$ of fluid X (density $\rho$) with a mass $M$ of fluid Y (density $3\rho$). Assuming the volumes are additive, which expression represents the density of the resulting mixture?

- (A) $1.5\rho$
- (B) $2.0\rho$
- (C) $0.75\rho$
- (D) $3.0\rho$

**Answer: (A)** Total mass is $2M$. Volume of X is $M/\rho$, Volume of Y is $M/3\rho$. Total Volume is $4M/3\rho$. Density = $2M / (4M/3\rho) = 1.5\rho$.

## Review the Unit

- [8.1 Internal Structure and Density](/ap-physics-1-revised/unit-8/1-internal-structure-and-density/study-guide/DMBG99gohfrckZfi)
- [8.2 Pressure](/ap-physics-1-revised/unit-8/2-pressure/study-guide/Fx7jEVnQ1A8HJIxq)
- [8.3 Fluids and Newton's Laws](/ap-physics-1-revised/unit-8/3-fluids-and-newtons-laws/study-guide/PbLGJiZX2gzaitf5)
- [8.4 Fluids and Conservation Laws](/ap-physics-1-revised/unit-8/4-fluids-and-conservation-laws/study-guide/KExgGEoV6YLUwBoa)

## Other Unit Tests

- [Unit 1: Kinematics](/ap-physics-1-revised/unit-test/1)
- [Unit 2: Force and Translational Dynamics](/ap-physics-1-revised/unit-test/2)
- [Unit 3: Work, Energy, and Power](/ap-physics-1-revised/unit-test/3)
- [Unit 4: Linear Momentum](/ap-physics-1-revised/unit-test/4)
- [Unit 5: Torque and Rotational Dynamics](/ap-physics-1-revised/unit-test/5)
- [Unit 6: Rotating Systems: Energy & Momentum](/ap-physics-1-revised/unit-test/6)
- [Unit 7: Oscillations](/ap-physics-1-revised/unit-test/7)

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