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Concepts Of Physics MCQ Edition [Volume 1]PhysicsNewton's Laws of Motion

Travelling at 40 km/h , a car must be brought to a halt by applying brakes within the next 4.0 m . Given that the car weighs 2000 kg , determine the average force that must be applied to it.

Options

  1. A6.2 10^4 N
  2. B4.0 10^5 N
  3. C5.6 10^3 N
  4. D3.1 10^4 N

Correct answer

D. 3.1 10^4 N

Step-by-step solution

Initial velocity, u = 40 km/h = 40 5 18 m/s = 100 9 m/s Final velocity, v = 0 Distance, s = 4.0 m Mass, m = 2000 kg Using the third equation of motion: v^2 - u^2 = 2as 0 - ( 100 9 )^2 = 2a(4.0) a = - 10000 81 8 = - 1250 81 m/s ^2 Average retarding force is given by F = m|a| : F = 2000 1250 81 = 2500000 81 N F 30864 N 3.1 10^4 N

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