`Uniform-Motion Problems: Just Playing With CarsDavid 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 theybe 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 andsolve 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. andmeasure 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 andwhere will the two cars meet?".  Set the cars on opposite sides of the room andlet 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 = 12.29They 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 themat 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.) `
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