Answer
a). Graph is shown,
b). 10 m/s
c). 237.5m
d). 16.96 m/s
Work Step by Step
a). graph is as shown.
b). $v=u+at$
$v=25-5\times 3=25-15=10 m/s$
c). in first 5s, s=$25 \times 5= 125m$
in second 3s, s=$ut+\frac{1}{2}at^{2}=25\times3-0.5\times 5\times 3^{2}=52.5m$
for the next 6s, s=$6\times 10=60m$
So, total displacement = $125+52.5+60=237.5m$
d). Average speed = $\frac{total\, distance}{total\, time}=\frac{237.5}{14}=16.96 m/s$