Kinematics Review

Vocabulary

100

What does "acceleration" mean?

Rate of change of velocity

200

What's the difference between distance and displacement?

Distance = total path length (scalar)

Displacement = straight line from start to finish (vector)

300

What is "kinematics"?

The study of motion (without considering forces).

400

What does "at rest" mean in a physics problem?

Velocity = 0

500

An object moves at a constant speed in a circle.

Is its velocity constant? Is it accelerating?

Velocity NOT constant

YES accelerating

Scalars/Vectors

100

Is speed a scalar or vector quantity?

Scalar

200

Is acceleration a scalar or vector quantity?

Vector

300

Name two vector quantities in kinematics.

Velocity, acceleration, displacement (any two)

400

A car goes 60 km east, then 40 km west.

Is the total distance a scalar or vector? What about total displacement?

Distance = scalar

Displacement = vector

500

Can a vector quantity ever be negative? What does that mean?

Yes, negative means opposite the chosen positive direction

Units

100

What are the units for distance or displacement?

m (meters)

200

What are the units for speed or velocity?

m/s (meters per second)

300

A problem gives distance in kilometers and time in hours.

What units will velocity have?

km/h (kilometers per hour)

400

You calculate an acceleration of 15.

What units must this be to make sense in physics?

m/s² (or any distance/time² unit)

500

What units would you get from multiplying acceleration (m/s²) by time (s)?

m/s (which is velocity!)

Equations

100

You need to find final velocity (v_f). You know initial velocity (v_i), acceleration (a), and time (t).

Which equation do you use?

II.

v_f = vᵢ + a*t

200

You need to find displacement (d). You know v_i, a, and t, but NOT final velocity (v_f).

Which equation do you use?

I.

d = vᵢ*t + ½*a*t²

300

You need to find acceleration (a). You know vᵢ, v_f, and d, but NOT time (t).

Which equation do you use?

III.

v_f² = vᵢ² + 2*a*d

400

A ball is thrown upward. You need to find maximum height. You know vᵢ, and a = -9.8 m/s². (v_f = 0 at top)

Which equation do you use?

III.

v_f² = vᵢ² + 2*a*d (with v_f = 0)

500

You need to find time (t). You know vᵢ, v_f, and d, but NOT acceleration (a).

Which equation do you use? 

IV.

d = ½(vᵢ + v_f)*t

Problems

100

A car goes 60 km east, then 40 km west.

Which has a larger value, the distance or displacement?

Distance is larger.

Distance = 100 km.

Displacement = 20 km east.

200

An object is dropped from rest (vᵢ = 0) and accelerates downward at 10 m/s² for 2 seconds. 

Using I. d = vᵢ*t + ½*a*t², what is the displacement?

d = (0 m/s)*(2s) + ½(10 m/s²)(2 s)²

d = 20 m downward

300

A bike accelerates from 5 m/s at 3 m/s² for 4 seconds.

Using II. v_f = vᵢ + a*t, find final velocity.  

v_f = 5 m/s + (3 m/s²)*(4 s)

v_f = 17 m/s (no direction given)

400

A car moving at 20 m/s brakes to stop over 40 m. After stopping, final velocity = 0.

Using III. v_f² = vᵢ² + 2*a*d, find acceleration. 

(0 m /s)² = (20 m/s)² + 2*a*(40 m)

a = (-400 m²/s²) / (80 m)

a = -5 m/s² (direction is opposite to car's motion)

500

A ball is thrown upward at 15 m/s. Acceleration from gravity is 10 m/s² downward, and the ball at its highest point has a final velocity of 0 m/s.

Using III. v_f² = vᵢ² + 2*a*d, find maximum height.

(0 m/s)² = (15 m/s)² + 2*(-10 m/s²)*d

d = (225 m²/s²) / (20 m/s²)

d = 11.25 m