Answers

2016-04-06T15:42:34+05:30
For the car,

Mass, m = 1200 kg
Initial Velocity, u = 54 km/h = 15 m/s
Final velocity, v = 0m/s

By Work Energy Theorem,

Work Done=Change in Kinetic Energy
∴W = ΔK                (If you don't understand this line, ignore it)
∴W = 1/2 mv² - 1/2 mu²
      = 1/2 m (v² - u²)
      = 1/2 * 1200 (0² - 15²)
      = 600 (0-225)
      = 600 * -225
∴W = -135,000 J  or  -135 kJ

Thus the Work required to stop the car is -135,000 Joule  or -135 kilo Joule.

The negative sign indicates that the work done is in the opposite direction.
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