b$.$ Water flows in a gully with a mean velocity $U\frac{m}{s}.$ Draw the Velocity Profile of this flow $($assuming the

flow is turbulent and not laminar$),$ showing points of minimum and maximum flow. What is the value

of the flow velocity at the bed of the gully?

c$.$ What happens to the viscosity of a liquid when it is heated? As a practical example of your answer,

briefly explain why it is recommended to change petroleum$-$based oils in a car every $3,000km.$