Return to Mathematics IndexUniform-Motion Problems: Just Playing With Cars

David Drymiller Morgan Park High School

1744 W. Pryor

Chicago IL 60643

(312)535-2550Objectives:

To solve uniform motion word problems using rate X time = distance.

To practice measuring in the metric and English systems.Materials Needed:

At least two battery operated cars with constant velocity,

Measuring tape with both English and metric systems at least 50 feet or

15 meters, meter and yard sticks,

Stop Watches at least two or more if possible,

masking tape

Strategy:

The students perform the following demonstration for their classmates under the

direction of the classroom teacher. No prior knowledge of the activity is

needed by the students.

First, with masking tape mark the starting and finishing lines for calculating

velocity over a fixed distance. (I used 800 cm.) Find the time needed for each

car to transverse the fixed distance. Record the time and distance on the

blackboard and then calculate the velocity of each car.

(25 cm/sec and 36 cm/sec)

Now introduce the first type of Uniform-Motion Problem, "If the cars are place

back to back and travel at the same time in opposite directions, when will they

be 1000 cm apart?". Explain the problem first as the cars are placed on the

floor back to back and run off in opposite directions. Next use the standard

associated pictures and charts for this type of problem, write the equation and

solve it in the usual manner.

25t + 36t = 1000

61t = 1000

t = 16.39

Place the cars back to back on the floor and let them run for 16.4 secs. and

measure the distance between the two cars. (It should work. I got 1020 cm.)

Now introduce the second type of Uniform-Motion Problem, "If the two cars are

750 cms apart and they each travel towards each other at the same time, when and

where will the two cars meet?". Set the cars on opposite sides of the room and

let them run into each other as you begin your explanation. Again use the

standard associated pictures and charts for this type of problem, write the

equation and solve it in the usual manner.

25t + 36t = 750 (12.29)(25) = 307.25 cm

61t = 750

t = 12.29

They should collide in approximately 12 secs, 307 cm from where the slower car

starts. Mark that spot on the floor. Place the cars 750 cms apart and run them

at each other. (I missed by 6 cm.)

Performance Assessment:

With two faster cars mark the starting and finishing lines for calculating

the velocity over a fixed distance. (I used 20 yards.) Also mark two starting

lines on opposite ends of the hallway. (65 yards) In teams of 3 or 4, the

students find the velocities, make the associated picture and chart, write the

equation and solve it in the usual manner, and mark the spot in the hall where

the two cars will collide. (This is competition at its best.)