Author Topic: Methods Qns I am stuck on (Read 723 times) Tweet Share

IntoTheNewWorld · « **on:** May 11, 2009, 08:20:26 pm »

Hi these are a few qns from a SAC I'm doing (ignore finger at bottom of page)

I'm currently unsure about qn 1 (ii)
...Any help for any of the other questions apart from 1 (i) would also be greatly appreciated =]

kamil9876 · « **Reply #1 on:** May 11, 2009, 08:44:20 pm »

1.) find dy/dx. then use the chain rule:

$\frac{dy}{dx} \frac{dx}{dt}= \frac{dy}{dt}$

kamil9876 · « **Reply #2 on:** May 11, 2009, 08:54:49 pm »

1. ii:

Refer to attatched diagram. By looking at similair triangles we see:
$<br />\frac{y+x}{6}=\frac{x}{2}$
$y+x=3x$
$y=2x<br />$
$\frac{dy}{dx}=2$

$\frac{dy}{dt}=24$ since the distance between him and the lamp is increasing at that rate.

Now use the chain rule to find $dx/dt$ by relating the two derivatives above. dx/dt is the rate at which the shadow lengthens.

b.) let y+x=u, we are after du/dt now.

$\frac{d}{dt}u=\frac{d}{dt}(y+x)=\frac{d}{dt}(x)+\frac{d}{dt}(y)$

These values you know from previous questions. Intuitively you could have said that its simply the addition of two velocity vectors, if this was a physics question

Search the forums now!

We have moved!

Author Topic: Methods Qns I am stuck on (Read 723 times) Tweet Share

IntoTheNewWorld

Methods Qns I am stuck on

kamil9876

Re: Methods Qns I am stuck on

kamil9876

Re: Methods Qns I am stuck on

Recent Posts

User:
Password: