You put a 3 kg block in the box, so the total mass is now 9 kg, and you launch this heavier box with an initial speed of 5 m/s. How long does it take to stop? Δt = s

Δt=0.85 seconds

Explanation:

In this chase the speed does not change as the mass change.So we can use the follow equation to find the required time

Δt=Δv/gμ

To stop the final speed will be zero therefore the change in speed will be

Δv= vf-vi

Δv=0-5 m/s

Δv= -5 m/s

Now we plug our values for  Δv,g and μ to find time

Δt=Δv/gμ

Δt=(-5m/s) ÷(9.8m/s² × 0.6)

Δt=0.85 seconds

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there are no components of a physical goal mentioned on the list of choices that you've provided.