AP Physics 1 practice problems: cram pack

Formula sheets, the key method steps for every topic and 14 practice problems, with full solutions at the back.

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1Formulas and methods

Kinematics

Velocity
v = v0 + a·t
Displacement
s = v0·t + ½·a·t²
Without time
v² = v0² + 2·a·s
Units
1 m/s = 3.6 km/h

Method

  1. List what you know: v₀, v, a, t and s, with units.
  2. Pick the equation that contains your three knowns and the unknown.
  3. Choose one positive direction and give opposing quantities a minus sign.
  4. Solve and check that the answer is physically sensible.

Newton’s laws

Second law
ΣF = m·a
Weight
W = m·g
Kinetic friction
Ff = μ·N
On a slope
along: m·g·sin θ, normal: m·g·cos θ

Method

  1. Draw a free-body diagram with every force on the body.
  2. Choose a positive direction along the motion.
  3. Split forces into components along and perpendicular to the motion (on a slope: m·g·sin θ along, m·g·cos θ into the slope).
  4. Apply ΣF = m·a along the motion; friction is μ·N against the motion.

Projectile motion

Components
vx = v0cos θ, vy = v0sin θ
Position
x = vxt, y = h + vyt − ½gt²
Maximum height
H = h + vy²/(2g)
Range (level ground)
R = v0²·sin 2θ/g

Method

  1. Split the launch velocity into components: vx = v₀·cos θ and vy = v₀·sin θ.
  2. The horizontal motion has constant speed; the vertical motion has acceleration −g.
  3. Find the time of flight from the vertical motion.
  4. Use that time in the horizontal motion to find the range.

Circular motion

Centripetal acceleration
a = v²/r = ω²·r
Centripetal force
F = m·v²/r
Angular speed
ω = v/r = 2π/T
Flat curve, friction
vmax = √(μ·g·r)

Work & energy

Kinetic energy
Ek = ½mv²
Potential energy
Ep = mgh
Energy balance
Ek1 + Ep1 + W = Ek2 + Ep2 + losses
Work of friction
W = μ·N·d
Power
P = W/t

Momentum & collisions

Momentum
p = m·v
Conservation
Σm·v (before) = Σm·v (after)
Perfectly inelastic
v′ = (m1v1 + m2v2)/(m1 + m2)
Impulse
J = F·Δt = m·Δv

Method

  1. Choose a positive direction and give each velocity its sign.
  2. Write the total momentum before: Σm·v.
  3. For a perfectly inelastic collision the bodies move together after; for an elastic one kinetic energy is also conserved.
  4. Set momentum before equal to momentum after and solve.

Springs & pendulums

Mass on a spring
T = 2π·√(m/k)
Pendulum
T = 2π·√(L/g)
Angular frequency
ω = √(k/m) = 2π/T
Maximum speed and acceleration
vmax = A·ω, amax = A·ω²
Energy
E = ½·k·A²

2Practice problems

1.KinematicsMedium
t (s)v (m/s)1.5 s22.22

A driver moving at 80 km/h sees an obstacle. Her reaction time is 1.5 s, after which the car brakes with a constant deceleration of 8 m/s². Find the total stopping distance d from the moment she sees the obstacle.

v₀ = 80 km/htr = 1.5 sa = −8 m/s²
d = m
2.KinematicsHard
d = ?

A stone is dropped from rest into a well. The splash is heard 2 s after the stone is released. The speed of sound is 343 m/s; ignore air resistance and use g = 9.81 m/s². Find the depth d of the well.

ttotal = 2 svsound = 343 m/sg = 9.81 m/s²
d = m
3.Newton’s lawsMedium
θ = 25°a = ?m = 12 kg

A 12 kg block slides down a slope at 25° to the horizontal. The coefficient of kinetic friction is 0.2. Use g = 9.81 m/s². Find the acceleration a of the block along the slope.

m = 12 kgθ = 25°μ = 0.2g = 9.81 m/s²
a = m/s²
4.Newton’s lawsHard
2 kg8 kgTF = 70 Nμ = 0.2

Two blocks on a level floor are joined by a light horizontal string. A horizontal force of 70 N pulls the front 8 kg block; the 2 kg block is towed behind. The coefficient of kinetic friction is 0.2 for both blocks. Use g = 9.81 m/s². Find the acceleration a of the blocks.

m1 = 2 kgm2 = 8 kgF = 70 Nμ = 0.2g = 9.81 m/s²
a = m/s²
5.Projectile motionMedium
v0​ = 32 m/sθ = ?R = 45 m

A ball is launched from level ground at 32 m/s and must land 45 m away. Ignore air resistance and use g = 9.81 m/s². Find the smaller of the two possible launch angles θ.

v₀ = 32 m/sR = 45 mg = 9.81 m/s²
θ = °
6.Projectile motionHard
25 mv0​ = 34 m/s65°x = ?

A ball is thrown from ground level at 34 m/s and 65° above the horizontal. It lands on the flat roof of a building 25 m high, on its way down. Ignore air resistance and use g = 9.81 m/s². Find the horizontal distance x from the launch point to where it lands.

v₀ = 34 m/sθ = 65°hroof = 25 mg = 9.81 m/s²
x = m
7.Circular motionMedium
L = 1.8 m30°

A small ball on a string of length 1.8 m moves in a horizontal circle so that the string makes a constant angle of 30° with the vertical (a conical pendulum). Use g = 9.81 m/s². Find the speed v of the ball.

L = 1.8 mθ = 30°g = 9.81 m/s²
v = m/s
8.Circular motionHard
r = 0.9 mv = ?

A ball on a string 0.9 m long is swung in a vertical circle. Use g = 9.81 m/s². What is the smallest speed vmin at the top for which the string just stays tight?

r = 0.9 mg = 9.81 m/s²
vmin = m/s
9.Work & energyMedium
90 km/h4°1800 kg

A 1800 kg car drives up a 4° slope at a constant 90 km/h. Air resistance and rolling resistance together amount to 400 N. Find the power P the wheels must deliver, in kW.

m = 1800 kgθ = 4°Fr = 400 Nv = 90 km/hg = 9.81 m/s²
P = kW
10.Work & energyHard
8 kg4 kgμ = 0.4d = 0.5 m

An 8 kg block rests on a rough horizontal table (μ = 0.4). A light string runs from it over a smooth pulley at the edge of the table to a hanging 4 kg block. The system is released from rest. Find the speed v of the blocks after the hanging block has dropped 0.5 m.

m1 = 8 kgm2 = 4 kgμ = 0.4d = 0.5 mg = 9.81 m/s²
v = m/s
11.Momentum & collisionsMedium
2 kgv = ?20 gh = 24 cm

A 20 g bullet is fired horizontally into a 2 kg wooden block hanging on light strings, and stays inside it. The block swings up until it is 24 cm higher than at the start. Use g = 9.81 m/s². Find the speed v of the bullet before impact.

m = 20 gM = 2 kgh = 24 cmg = 9.81 m/s²
v = m/s
12.Momentum & collisionsHard
19 m/s16 m/s

A 0.15 kg ball hits a wall at 19 m/s and bounces straight back at 16 m/s. The contact lasts 50 ms. Find the magnitude of the impulse J the wall gives the ball.

m = 0.15 kgvin = 19 m/svout = 16 m/sΔt = 50 ms
J = N·s
13.Springs & pendulumsMedium
L = ?

How long must a simple pendulum be to have a period of 2 s? Use g = 9.81 m/s². Find L.

T = 2 sg = 9.81 m/s²
L = m
14.Springs & pendulumsHard
1.2 kgk = 480 N/mA = 11 cm

A 1.2 kg mass on a spring with k = 480 N/m is pulled 11 cm from equilibrium and released. Find its maximum speed vmax.

m = 1.2 kgk = 480 N/mA = 11 cm
vmax = m/s

3Solutions

1.Kinematics

Answer: d = 64.2 m

Motion with constant acceleration: v = v₀ + a·t, s = v₀·t + ½·a·t² and v² = v₀² + 2·a·s. Pick the equation that contains the three things you know and the one you want, and keep the signs consistent with one positive direction.

Units

v₀ = 80/3.6 = 22.22 m/s

Reaction distance

d1 = v₀·tr = 22.22·1.5 = 33.33 m

Braking distance

d2 = v₀²/(2a) = 22.22²/(2·8) = 30.86 m

Total

d = 33.33 + 30.86 = 64.2 m

Answer

d = 64.2 m
2.Kinematics

Answer: d = 18.57 m

Motion with constant acceleration: v = v₀ + a·t, s = v₀·t + ½·a·t² and v² = v₀² + 2·a·s. Pick the equation that contains the three things you know and the one you want, and keep the signs consistent with one positive direction.

Two parts of the time

½·9.81·t₁² = 343·(2 − t₁)
4.905·t₁² + 343·t₁ − 686 = 0

Fall time

Only the positive root is physical.

t₁ = (−343 + √(343² + 4·4.905·686))/(2·4.905) = 1.946 s

Depth

d = ½·9.81·1.946² = 18.57 m

Answer

d = 18.57 m
3.Newton’s laws

Answer: a = 2.368 m/s²

Newton’s second law: the net force on a body equals its mass times its acceleration, ΣF = m·a. Draw a free-body diagram, choose a positive direction along the motion, and add every force in that direction: applied forces, friction μ·N against the motion, and the components of gravity.

Forces along the slope

Down the slope is positive.

m·a = m·g·sin θ − μ·m·g·cos θ

Acceleration

a = 9.81·(sin 25° − 0.2·cos 25°) = 9.81·(0.4226 − 0.1813) = 2.368 m/s²

Answer

a = 2.368 m/s²
4.Newton’s laws

Answer: a = 5.038 m/s²

Newton’s second law: the net force on a body equals its mass times its acceleration, ΣF = m·a. Draw a free-body diagram, choose a positive direction along the motion, and add every force in that direction: applied forces, friction μ·N against the motion, and the components of gravity.

Whole system

a = (F − μ·(m1 + m2)·g)/(m1 + m2) = (70 − 19.62)/10 = 5.038 m/s²

Answer

a = 5.038 m/s²
5.Projectile motion

Answer: θ = 12.77 °

Projectile motion: with no air resistance, x = vxt and y = h + vyt − ½gt². The two directions are independent except that they share the same time.

Range formula

R = v₀²·sin 2θ/g → sin 2θ = 9.81·45/32² = 0.4311

Angle

2θ = 25.54° → θ = 12.77°

Answer

θ = 12.77°

The other solution is 90° − θ = 77.23°.

6.Projectile motion

Answer: x = 76.52 m

Projectile motion: with no air resistance, x = vxt and y = h + vyt − ½gt². The two directions are independent except that they share the same time.

Split the launch velocity

vx = 14.37 m/s, vy = 30.81 m/s

Time to land on the roof

Larger root: the ball is descending.

25 = 30.81·t − 4.905·t²
t = (30.81 + √(30.81² − 2·9.81·25))/9.81 = 5.325 s

Horizontal distance

x = vx·t = 14.37·5.325 = 76.52 m

Answer

x = 76.52 m
7.Circular motion

Answer: v = 2.258 m/s

Uniform circular motion: an object moving at speed v on a circle of radius r accelerates towards the centre with a = v²/r, so it needs a net inward force F = m·v²/r. That force is supplied by something real: friction, tension, gravity or a normal force.

Radius of the circle

r = L·sin θ = 1.8·sin 30° = 0.9 m

Speed

Tension and gravity together give the inward force: tan θ = v²/(r·g).

v = √(r·g·tan θ) = √(0.9·9.81·tan 30°) = 2.258 m/s

Answer

v = 2.258 m/s
8.Circular motion

Answer: vmin = 2.971 m/s

Uniform circular motion: an object moving at speed v on a circle of radius r accelerates towards the centre with a = v²/r, so it needs a net inward force F = m·v²/r. That force is supplied by something real: friction, tension, gravity or a normal force.

Tension zero at the top

m·g = m·v²/r → v = √(g·r) = √(9.81·0.9) = 2.971 m/s

Answer

vmin = 2.971 m/s
9.Work & energy

Answer: P = 40.79 kW

Work–energy principle: the change in kinetic energy equals the work done by all forces. Writing gravity and springs as potential energy (mgh and ½kx²) turns this into a balance: initial energy = final energy + energy lost to friction (μN·d). Power is force times speed: P = F·v.

Driving force

m·g = 1800·9.81 = 17658 N
mg·sin θ = 17658·sin 4° = 1232 N
F = 1232 + 400 = 1632 N

Power

v = 90/3.6 = 25 m/s
P = F·v = 1632·25 = 40794 W = 40.79 kW

Answer

P = 40.79 kW
10.Work & energy

Answer: v = 0.8087 m/s

Work–energy principle: the change in kinetic energy equals the work done by all forces. Writing gravity and springs as potential energy (mgh and ½kx²) turns this into a balance: initial energy = final energy + energy lost to friction (μN·d).

Energy released and lost

m₂g·d = 39.24·0.5 = 19.62 J
μ·m₁g·d = 0.4·78.48·0.5 = 15.7 J

Kinetic energy of both blocks

½(m₁ + m₂)v² = 3.924 → v = √(2·3.924/12) = 0.8087 m/s

Answer

v = 0.8087 m/s
11.Momentum & collisions

Answer: v = 219.2 m/s

Conservation of momentum: when no external force acts during a collision, the total momentum Σm·v before equals the total after. Velocities have a direction, so pick a positive direction and give velocities the other way a minus sign. In an elastic collision kinetic energy is conserved too; in a perfectly inelastic one the bodies stick together.

Swing after impact

V = √(2·g·h) = √(2·9.81·0.24) = 2.17 m/s

Collision

m·v = (m + M)·V → v = (0.02 + 2)·2.17/0.02 = 219.2 m/s

Answer

v = 219.2 m/s
12.Momentum & collisions

Answer: J = 5.25 N·s

Conservation of momentum: when no external force acts during a collision, the total momentum Σm·v before equals the total after. Velocities have a direction, so pick a positive direction and give velocities the other way a minus sign. In an elastic collision kinetic energy is conserved too; in a perfectly inelastic one the bodies stick together.

Change in momentum

J = m·Δv = 0.15·(16 + 19) = 5.25 N·s

Answer

J = 5.25 N·s
13.Springs & pendulums

Answer: L = 0.994 m

Simple harmonic motion: a mass m on a spring of stiffness k oscillates with angular frequency ω = √(k/m) and period T = 2π/ω = 2π·√(m/k). A simple pendulum of length L has T = 2π·√(L/g). With amplitude A, the largest speed is A·ω, the largest acceleration A·ω² and the energy ½·k·A².

Solve for the length

L = g·(T/2π)² = 9.81·(2/2π)² = 0.994 m

Answer

L = 0.994 m
14.Springs & pendulums

Answer: vmax = 2.2 m/s

Simple harmonic motion: a mass m on a spring of stiffness k oscillates with angular frequency ω = √(k/m) and period T = 2π/ω = 2π·√(m/k). A simple pendulum of length L has T = 2π·√(L/g). With amplitude A, the largest speed is A·ω, the largest acceleration A·ω² and the energy ½·k·A².

Angular frequency

ω = √(480/1.2) = 20 rad/s

Maximum speed

vmax = A·ω = 0.11·20 = 2.2 m/s

Answer

vmax = 2.2 m/s

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