Motion Word Problems

Speed Versus Velocity

Speed describes how fast something is moving. It is a scalar quantity (does NOT indicate direction).

Even though some questions may ask you to calculate the average “velocity”, if you are given the total distance traveled and the time it took, you are actually calculating the SPEED.

If you are given the displacement (where you finished compared to where you started) along with the direction, then you are calculating velocity.

d

s t

d

v t

t

v

a

You NEED to know these equationsSpeed = distance ÷ time distance = speed X time Time = distance ÷ speedVelocity = displacement ÷ time Displacement = velocity X time Time = displacement ÷ velocity Acceleration = velocity ÷ time Velocity = acceleration X time Time = velocity ÷ acceleration

Steps when solving word problems

1. Write down what you know (example: d = 10 m & t = 5 sec.) and what you need to find (example: speed = ?)

2. Write down your equation (example: speed = d ÷ t)

3. Plug in what you know (example: speed = 10m ÷ 5sec.)

4. Solve, being sure to check your significant figures, and giving the proper units (example: speed = 2 m/sec.)

5. Check your work

Example #1High speed elevators can attain a speed

of 7.11m/s. How much time would they need to climb 37.5m (about 10 stories)?

Speed = 7.11 m/sDistance = 37.5 mTime = ?Time = distance ÷ speedTime = 37.5 m ÷ 7.11 m/sTime = 5.27 seconds

Example #2A cattle train left Halifax and traveled toward Toronto. Six hours

later a diesel train left traveling at 45 km/h in an effort to catch up to the cattle train. After traveling for five hours the diesel train finally caught up. What was the cattle train's average speed?

Speed (diesel) = 45 km/hTime (diesel) = 5 hoursDistance travelled (diesel) = ?Distance (diesel) = speed X timeDistance (diesel) = 45 km/h X 5 hoursDistance (diesel) = 225 km this is the distance where the trains

metTime (cattle) = 6 hours + 5 hours = 11 hoursSpeed (cattle) = distance / timeSpeed (cattle) = 225 km / 11 hoursSpeed (cattle) = 20 km/h