Question

What units do I use for the question:

How far does a lorry move if it is travelling at 15m/s for 20 mins

Answer 1

You can use any distance unit you want. But whatever unit you choose,
you'll need to EITHER change the 15 m/s and the 20 mins to be consistent
before you multiply them, OR change the answer to your chosen unit after
you multiply.

Examples:

#1). I choose the unit of meters.

(20 mins) x (60 sec/min) = 1200 sec

(15 m/s) x (1200 sec) = (15 x 1200) m-sec/sec = 18,000 meters .

= 18.0 kilometers


#2). I choose the unit of feet.

(15 mtr/s) x (3.28 ft/mtr) = 49.2 ft/sec

(49.2 ft/sec) x (20 min) x (60 sec/min)

= 59,055 feet x (1 mile / 5,280 ft)

= 11.2 miles

Answer 2

you should go for m/s, as it's S.I. UNIT

Speed = 15m/s

time = 1200 sec

distance = s * t = 15*1200 = 18000 m OR 18 Km