How Far Will You Go Before Stopping? Can You Avoid Hitting the Dog?

AI Thread Summary
When calculating stopping distance after seeing a dog on the road while driving at 90 km/h, a user initially arrived at an incorrect distance of 540m. The error stemmed from not converting the speed from kilometers per hour to meters per second before using the formula V^2 = Vi^2 + 2ad. After correcting the units, the user was advised to re-calculate the stopping distance. The conversation highlights the importance of unit conversion in physics problems. Accurate calculations are crucial for determining whether a driver can avoid hitting an obstacle.
ms. confused
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You are driving your new sports car at a velocity of 90km/hr, when you suddenly see a dog step into the road 50m ahead. You hit the brakes hard to get maximum deceleration of 7.5m/s^2. How far will you go before stopping? Can you avoid hitting the dog?

I got 540m, which I know is wrong. V=0; Vi=90; a= -7.5; d=? I plugged those values into this formula: V^2= Vi^2 + 2ad. What have I done wrong? Anyone? :redface:
 
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ms. confused said:
What have I done wrong?

Right here:

Vi=90

Check your units. The given value of vi is 90 km/h[/color], but you plugged it in as though it were 90 m/s. Convert the units and re-calculate. It should work.
 
Okay, got it...thanks for your help!
 
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