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This question makes use of the distance-rate-time formula.
The acceleration is constant, so we know the velocity goes from a starting speed to a final speed. The one variable we do know is distance.
Distance = rate x time
We know distance AND time.
It's just that the rate is changing - but it's changing at a constant rate of acceleration. Because of that we know there is an average speed. You can rewrite the equation as:
Distance = Avg speed x Time
Avg Speed = Distance / Time
= 525 m / 15s
= 35 m/s
OK, so that is the average speed. But we have to find the starting and final speed. OK...well the average of the starting and final speed will get us the average speed.
So, adding ("starting speed" + "final speed" ) / 2 = 35 m/s
So, "starting speed" + "final speed" = 70m/s
The only 2 possible answer choices whose sum is equal to 70m/s is 2m/s and 68m/s
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