How much work in joules must be done to stop a 5000 kg car traveling at 120 km/hr?

To calculate the work done to stop a car, we first need to find its initial kinetic energy and then subtract its final kinetic energy.

Step 1: Calculate initial kinetic energy:
The formula for kinetic energy is given by:
Kinetic Energy = 1/2 * mass * velocity^2

Given:
Mass of the car (m) = 5000 kg
Velocity of the car (v) = 120 km/hr

First, we need to convert the velocity from km/hr to m/s, as the formula requires the velocity to be in meters per second (m/s).
To convert, divide the velocity by 3.6:
120 km/hr / 3.6 = 33.33 m/s (rounded to two decimal places)

Using the formula for kinetic energy, we can now calculate the initial kinetic energy:
Initial Kinetic Energy (KE_initial) = 1/2 * mass * velocity^2
KE_initial = 1/2 * 5000 kg * (33.33 m/s)^2

Step 2: Calculate final kinetic energy:
Since we want to stop the car, its final kinetic energy will be zero (as it will come to rest). Therefore, the final kinetic energy (KE_final) is 0.

Step 3: Calculate the work done:
The work done to stop the car can be found by subtracting the final kinetic energy from the initial kinetic energy.
Work (W) = KE_initial - KE_final
W = KE_initial - 0
W = KE_initial

Now, we can substitute the calculated values into the equation:
W = (1/2) * 5000 kg * (33.33 m/s)^2

Let's calculate this:
W = 0.5 * 5000 * (33.33^2)

W ≈ 2,777,800 J

Therefore, the work done to stop the car is approximately 2,777,800 Joules.