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

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SUMMARY

The discussion centers on a physics problem involving a sports car traveling at 90 km/h and the calculation of stopping distance when decelerating at 7.5 m/s². The original poster incorrectly used the initial velocity in meters per second instead of kilometers per hour, leading to an erroneous stopping distance of 540 meters. After correcting the unit conversion, the proper approach to solving the problem was clarified, emphasizing the importance of consistent units in calculations.

PREREQUISITES
  • Understanding of basic kinematics
  • Familiarity with unit conversions (km/h to m/s)
  • Knowledge of the equations of motion, specifically V² = Vi² + 2ad
  • Ability to perform calculations involving acceleration and distance
NEXT STEPS
  • Learn about unit conversion techniques, particularly for speed measurements
  • Study the equations of motion in greater depth, focusing on practical applications
  • Explore real-world examples of braking distances in automotive safety
  • Investigate the effects of different deceleration rates on stopping distances
USEFUL FOR

Students studying physics, automotive engineers, and anyone interested in understanding vehicle dynamics and safety calculations.

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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