The unit ramp function has slope `1` [so the function is simply `V(t) = t`], starting from `t = 0` [so we need to multiply by `u(t)`], and passes through `(0, 0)`.
So the voltage function is given by:
`V(t) = t · u(t)`
The graph of the function is:
Graph of `V(t)=t · u(t)`, the unit ramp function.
Easy to understand math videos: