Why does a lorry travelling at 30mph have more kinetic energy than a car travelling at the same velocity?

Because it has more mass

Explanation:

To understand this, think about the equation of kinetic energy

KE = m

Kinetic energy depends on both the velocity (v) as well as the mass (m).

Because a lorry is bigger and heavier than a car, it will have more mass. With more mass, at the same velocity the lorry with have more kinetic energy.