Question

Repost...see attached on speed-time graph. Qn part d.

Answer 1

lol i saw this question earlier, wanted to solve it but it looks so tedious. Oh well, i will do it now.

Answer 2

pls try...thank you.

Answer 3

First you find the difference in the area under graph from t=0 to t=15.
So go ahead to find the distance travelled by the truck till t=15
and the car till t=15.

For the car= area of the triangle= 0.5 * (15-5)*20= 100

For the truck + area of triangle + area of trapezium= 0.5*12*6+0.5* (12+16)* (15-6)
=162

Difference in distance traveled = 162-100 = 62

So this 62 is referring to the trapezium, from t=15 onwards for the area between the car and the truck speed-line.

Let T be the time after 15 secs when the car just overtake the truck.
area of trapezium = 62= 0.5*T* [2(T+10) + (20-16)]
124= T * 2T+20+4
124= 2T^2 +24T
2T^2 +24T - 124=0
T= 3.89

Thus the time when car overtake truck is 3.89+15 = 18.9s approximately.
Do you have the answer? Can double check if i made any mistake. The method should be correct.
I know it can be quite confusing so if you are not sure, just ask.

Answer 4

Yours is the last question im doing before i go off. So just go through and make sure you ask now, if not no chance alrdy. haha btw are u singapore? this question paper seems familiar to me.

Answer 5

yep...sgrean...give me a min to browse thru..thx

Answer 6

don't have answer sheet...hopefully is correct. Thank you for your time...good nite!

Answer 7

no la not sleeping yet. Just want to stop looking at people's questions. What level is this? anw i really hate these kind of questions. It doesnt test your concept, it just makes things difficult for you to do things and hoping you make a careless mistake.

Answer 8

but for part c..v= 20? i got 30 instead however, i understand your steps and seems right. It's O level paper lor...stupid prelim paper

Answer 9

yea its v=20. Note that the slope/acceleration of the car from 5 to 15s is similar to the acceleration of the truck from t=0 to t=6. Since at t=6, the truck's speed is 12, we know the acceleration is 2.
So from t=5 to t=15 is 10s. in 10s, at acceleration of 2. the final speed would be 2*10= 20 m/s

Answer 10

oh ya...i forget to minus 5..no wonder...tq tq...