A football quarterback runs 25.0m straight down the field in 3.5s. He is hit by an opposing player and pushed 3.0m back in 1.75s. He breaks the tackle and runs another 24.0m in 4.2s. What was his average speed for the complete run from start to finish? -1.71 m/s -7.14 m/s 4.29 m/s 1.71 m/s -2.52 m/s 4.87 m/s 7.14 m/s
The Correct Answer and Explanation is:
To find the quarterback’s average speed for the complete run, we need to calculate the total distance traveled and the total time spent. Then we can use the formula for average speed:Average speed=Total distanceTotal time\text{Average speed} = \frac{\text{Total distance}}{\text{Total time}}Average speed=Total timeTotal distance
Step 1: Calculate Total Distance
The quarterback moves in three distinct phases:
- First phase: Runs 25.0 m straight down the field.
- Second phase: Is pushed back by 3.0 m.
- Third phase: Breaks the tackle and runs 24.0 m.
Total distance traveled is the sum of the absolute values of these displacements:Total distance=25.0 m+3.0 m+24.0 m=52.0 m\text{Total distance} = 25.0 \, \text{m} + 3.0 \, \text{m} + 24.0 \, \text{m} = 52.0 \, \text{m}Total distance=25.0m+3.0m+24.0m=52.0m
Step 2: Calculate Total Time
The total time taken for the three phases is:
- First phase: 3.5 seconds.
- Second phase: 1.75 seconds.
- Third phase: 4.2 seconds.
Total time taken is:Total time=3.5 s+1.75 s+4.2 s=9.45 s\text{Total time} = 3.5 \, \text{s} + 1.75 \, \text{s} + 4.2 \, \text{s} = 9.45 \, \text{s}Total time=3.5s+1.75s+4.2s=9.45s
Step 3: Calculate Average Speed
Now, we can use the formula for average speed:Average speed=Total distanceTotal time=52.0 m9.45 s≈5.5 m/s\text{Average speed} = \frac{\text{Total distance}}{\text{Total time}} = \frac{52.0 \, \text{m}}{9.45 \, \text{s}} \approx 5.5 \, \text{m/s}Average speed=Total timeTotal distance=9.45s52.0m≈5.5m/s
So, the quarterback’s average speed is approximately 5.5 m/s, but this value doesn’t match exactly with any of the choices listed, though the closest given option is 4.87 m/s. This might be a rounding or simplification issue in the options. Nevertheless, 5.5 m/s represents the correct calculation based on the provided data.
