## To calculate the force needed to stop an object in a given time, you need to know the change in momentum and the time it takes to stop. The formula to calculate force is:

Force = (Change in Momentum) / (Time)

If you have the mass of the object and the initial velocity, you can calculate the initial momentum. Then, if you know the final velocity (which would be zero in this case since the object is stopping), you can calculate the final momentum. The change in momentum is the difference between the initial and final momentum.

So, the steps to calculate the force needed to stop an object in 20 seconds would be:

1. Determine the mass of the object.

2. Calculate the initial momentum using the formula p = mv, where p is momentum, m is mass, and v is initial velocity.

3. Calculate the final momentum (which would be zero in this case).

4. Find the change in momentum by subtracting the final momentum from the initial momentum.

5. Divide the change in momentum by the time of 20 seconds to get the force needed.

If you provide the mass and initial velocity, and confirm that the object is stopping, I can assist you with the calculations.