Given,
a=6t−12u=9 m/s
Distance travelled in 5 s=7x
As we know.
a=dvdt...(i)adt=dv
Integrating both sides by putting the values we get,
∫v9=dv=∫t0(6t−12)dtv−9=3t2−12tv=3t2−12t+9=0
at t=1 s and t=3 s
As we know,
v=dsdt...(ii)dsdt=∫533t2−12t+9∫s0ds=∫53(3t2−12t+9)dt
Hence,
s=∣∣∫(3t2−12t+9)10 dt∣∣+∣∣∫(3t2−12t+9)31 dt∣∣+∣∣∫(3t2−12t+9)53∣∣dts=28m
Therefore,
7x=28x=4m