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A car and driver weighing 7750 N passes a sign stating “Bridge Out 28.5 m Ahead.” She slams on the brakes, and the car decelerates at a constant rate of 10.6 m/s2 .
The acceleration of gravity is 9.8 m/s2 .
What is the magnitude of the work done stopping the car if the car just stops in time to avoid diving into the water?
Answer in units of J

  • physics -

    Using Newton's second law F=ma
    to find the mass, then again the same law to find the frictional force.
    Finally use Work done = F.D
    Units are in kg, m/s² and J.

    Mass m = 7750/9.8 = 790.82 kg
    Frictional force = ma
    = 790.82 kg * 10.6 m/s²
    = 8382.7 N

    Work done (assuming uniform frictional foce)
    = F.D
    = 8382.7 N * 28.5 m
    = 238906 J
    = 238.9 kJ

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