Question

A car of 900 kg mass is moving at the velocity of 60 km/hr. It is brought into rest at 50 meter distance by applying a brake. Now, calculate the force required to stop the car.

Answers

  1. Answer: -2502N

    Explanation:

    (V_2)^2=(V_1)^2+2ad

    where;

    V_2 = final velocity = 0

    V_1 = initial velocity = 60 km/h = 16.67 m/s

    a = acceleration

    d = distance

    First all of, because acceleration is given in m/s and not km/h, you need to convert 60km/h to m/s. Our conversion factors here are 1km = 1000m and 1h = 3600s

    60km/h(\frac{1000m}{1km} )(\frac{1h}{3600s} )=16.67m/s

    Solve for a;

    (V_2)^2=(V_1)^2+2ad

    Begin by subtracting (V_1)^2

    (V_2)^2-(V_1)^2=2ad

    Divide by 2d

    \frac{(V_2)^2-(V_1)^2}{2d} =a

    Now plug in your values:

    a=\frac{(0)^2-(16.67 m/s)^2}{2(50m)}

    a=\frac{0-277.89m^2/s^2}{100m}

    a=-2.78m/s

    If you’re wondering why I calculated acceleration first is because in order to find force, we need 2 things: mass and acceleration.

    F=ma

    m = mass = 900kg

    a = acceleration = -2.78m/s

    F=(900kg)(-2.78m/s)\\F=-2502N

    It’s negative because the force has to be applied in the opposite direction that the car is moving.

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