1,000,000 Question Thread :D

[kenhung123]

Just another one of those threads lol.

[kenhung123]

I don't understand this question:

I did 1/2*20*(2+8)+10*10.5-20=185m

First I found the area of the first 8 seconds using the area of trapezium formula, then counted the square for the curved area then *10 as per square as value of 10, then the last triangle area minus 20.

If I count the squares then *10 it is accurately 11.5*10 which is 115m. It has 10 full squares and 3 half squares. Why is the displacement different when using the area of trapezium formula?

[Aden]

It is because the trapezium is only there from 0-6 seconds, you counted the squares until 8 seconds. If you look at the poorly edited attached image (sorry!), then you can count 7.5 squares (75m), and using the area of trapezium formula:

[vcesuccess]

Very confusing. Thanks for pointing it out. I thought it looked like trapezium too.

[kenhung123]

Thanks!
Can you help me on last question too?

[Aden]

According to the graph, the car is moving at a constant velocity from 4-12 seconds, so it undergoes no acceleration during this time ()

[kenhung123]

Thanks another one lol

[kriptik]

i think its good if you drew the graph and find their intersection, correct me if im wrong.

[kenhung123]

Yea, I attempted that.
I did:
80t=1/2*15*100+100(t-15)
t=37.5s

[Aden]

I have already done this question here:

http://vcenotes.com/forum/index.php/topic,21316.0.html

[kenhung123]

Hmm how did you know the acceleration changed form 10-15s?

[Aden]

Think about it logically, the car accelerated from 0km/hr to 80km/hr in ten seconds and then from 80km/hr to 100km/hr in five, that means in the first 10 seconds it gained 80hm/hr and in the next five seconds it gained 20km/hr. The car cannot have had a steady acceleration when it gained four times as much velocity in double the amount of time for the first ten seconds.

[kenhung123]

Oh! Silly me LOL!
Also, how do you know the variables are identical where you used t and (t-15)
Sometimes it doesnt satisfy though such as when t=10

[Aden]

I'm not sure I fully understand your question... =\

[kenhung123]

When x=1 the equation is false so it doesn't always satisfy. However how come we are allowed to use the same variables (x) on both sides? I guess its just my poor maths skills :S