We have that the average acceleration is
[tex]a=5m/s^2[/tex]
From the Question we are told that
Decreases his velocity from 20 m/s to 10 m/s in 2.0 s.\
Generally the equation for the average acceleration is mathematically given as
[tex]a=\frac{u-v}{t}\\\\a=\frac{20-10}{2}[/tex]
[tex]a=5m/s^2[/tex]
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