v=4t+11

s=2t^2+11t

(assuming it starts from 0)

At start of 2nd second (t=1) it is at 13m, at end of 2nd second (t=2) it is at

30m, so it has moved 30-13=17m.

Now you should be able to do the 8th second part.

Average speed is 21m/s, distance travelled in 7 seconds is 7*21=147.An object moving with a velocity of 42m/s is stopped in 7 seconds.

How far has it travelled?

Isn't that 42+36+30+24+18+12+6 = 168? But answer is 147.

(using the aversge speed works here if we assume constant decelleration).

RonL