what makes you walk?

Just had a HKUST interview through phone. Woke up early today just to prepare for that. It was a conference call with three person. The whole thing was quite good until they asked me

Interviewer Me

"What do you need to build a car that can travel 1000km per gasoline"

*SHIT*

"Low density material for the vehicle, so that it can travel at a high velocity. The shape must be aerodynamic, to reduce air resistance.. and errrr.. yea"

"What else? What kind of energy do you need? Like what makes you walk?"

*stoned for a few seconds*

"Workdone?"

"It's friction actually."

*Holyyyyy!!! *

IT'S FRICTION!!!!!!! I feel stupid now, for not getting this question answered correctly. We have learnt that since high school? ADUIIII WHYYYYYYY??? It was embarrassing. Workdone is energy! holy crap why on earth I answer that. Oh on.

The whole conversation was about 14 minutes. Slightly shorter than HKU ones. And this reminds me of the interview question I got during the HKU interview session.
"What is the definition of exponential square?"

seriously, why they ask so many weird weird question? dai lai this time.

Ok gotta study chemistry now!
BYE!