Practice Equilibrium in Physics

Use these practice problems to test your method after reviewing the concept explanation and worked examples.

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Quick Recap

A state in which all forces acting on an object balance so that the net force equals zero and there is no acceleration.

All forces cancel out — the object doesn't accelerate, though it may still be moving at constant velocity.

Showing a random 20 of 50 problems.

Example 1

medium

A box is pushed right at

12

N and stays still due to friction. What is the friction force?

A 12 N push cannot move the box — find the friction force keeping it still.

Example 2

hard

For

2\text{A} \rightleftharpoons \text{B}

with

K_1

, what is K for

4\text{A} \rightleftharpoons 2\text{B}

Example 3

medium

2

kg block rests on a

30^\circ

frictionless incline against a horizontal wall at its base. Is it in equilibrium without friction? Explain with the slope-direction net force.

Is this 2 kg block on a frictionless 30° incline in equilibrium? Identify the net slope-direction force.

Example 4

easy

For

\text{A}+\text{B} \rightleftharpoons \text{C}

, write the equilibrium expression

K

Example 5

medium

For

\text{H}_2 + \text{I}_2 \rightleftharpoons 2\text{HI}

, at equilibrium

[\text{H}_2] = 0.20\,\text{M}

[\text{I}_2] = 0.20\,\text{M}

[\text{HI}] = 1.00\,\text{M}

. Find

K

Example 6

easy

Which arrow symbol indicates a reversible reaction at equilibrium?

Example 7

medium

5

kg sign hangs from a single rope. A side wind pushes it horizontally with

30

N, holding the rope at an angle. Find the rope tension (

g=10

m/s

^2

Wind pushes 30 N right; rope holds sign at angle — find rope tension T (g

Example 8

easy

Is a system at chemical equilibrium static or dynamic?

Example 9

easy

Does "at equilibrium" mean the concentrations of reactants and products are necessarily equal?

Example 10

medium

For

\text{N}_2\text{O}_4 \rightleftharpoons 2\text{NO}_2

K = 0.211

at equilibrium

[\text{N}_2\text{O}_4] = 0.500\,\text{M}

. Find

[\text{NO}_2]

Example 11

medium

Given

\text{A} \rightleftharpoons \text{B}

with

K = 3.0

. At equilibrium

[\text{A}] = 0.20\,\text{M}

. Find

[\text{B}]

Example 12

easy

Three horizontal forces give equilibrium. Two are

5

N left and

3

N left. What is the third?

Two leftward forces (5 N and 3 N) act on an object — find F₃ for equilibrium.

Example 13

challenge

4

kg mass hangs from ropes A (horizontal) and B (at

30^\circ

above horizontal from a wall). Find tension in rope B (

g=10

m/s

^2

Rope A is horizontal, rope B at 30° above horizontal — find tension in rope B (g

Example 14

easy

A crate slides at a constant

3

m/s across a floor. Is it in equilibrium?

Example 15

easy

5

kg lamp hangs at rest from a cord (

g=10

m/s

^2

). What is the cord's tension?

Find the cord tension for a 5 kg lamp hanging at rest (g

Example 16

medium

10

kg traffic light hangs from two cables at

45^\circ

each from the horizontal (

g=10

m/s

^2

). Find each tension.

Two cables each at 45° from horizontal support a 10 kg traffic light — find each tension (g

Example 17

medium

6

kg block on a

30^\circ

incline is held at rest by a rope along the slope (

g=10

m/s

^2

, frictionless). Find the tension.

Find rope tension T to hold a 6 kg block on a frictionless 30° incline (g

Example 18

medium

An object is in equilibrium under three forces:

F_1 = 10 \text{ N}

east,

F_2 = 10 \text{ N}

north. What is the magnitude and direction of the third force

F_3

F₁

Example 19

challenge

For

\text{H}_2 + \text{I}_2 \rightleftharpoons 2\text{HI}

K = 50

. If

[\text{H}_2]_0 = [\text{I}_2]_0 = 1.00\,\text{M}

, no HI initially, find

[\text{HI}]

at equilibrium.

Example 20

challenge

A uniform

6

20

N beam is supported at both ends. A

60

N weight sits

2

m from the left end. Find the left support force.

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Related Concepts

Net Force Acceleration Statics Tension