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Thanks Alan, 

In Q2 it was a and d that confused me (not b and d)

SO I would still like you to discuss a please.

The question was

Which is NOT possible.

a) A body travels with a constant acceleration and a time varying velocity,

d) A body travels with a constant velocity and a time varying accelteration.

The words 'time varying ' confuse me

BUT consider d

Say the body was travelling in a circular motion.  Then the velocity could be contant and the acceleration would not be 0.  

If it was travelling in an curved path, couldn't it have a constant velocity and a time varying acceleration?

Another way to think of this question is as follows:

Imagine a sphere of radius, s.  The volume of this sphere is (4/3).pi.s³.

Imagine it is surrounded by a larger sphere of radius s+δs.  The volume of this sphere is (4/3).pi.(s+δs)³.

The volume of the shell between them is therefore (4/3).pi.(s+δs)³ - (4/3).pi.s³.

This shell volume is therefore: (4/3)*pi*(3.s².δs + 3.s.δs² + δs³)

Now we are going to shrink the thickness of this shell until we can ignore terms involving higher than linear powers of δs.  So an infinitesimal thickness shell will have a volume of 4.pi.s².ds  (where I've replaced δs by ds for the infinitesimal limit). Now the mass in this infinitesimally thin shell is just density*volume or

(1/s(1+s)³)*4.pi.s².ds

This is an infinitesimal mass, of course, so to get a non-infinitesimal mass we have to sum (integrate) this between one radius and another. The second radius is a non-infinitesimal distance away from the first. In this problem the question is clearly asking for the first radius to be zero and the second to be infinity. So the total mass is given by the integral shown in my first reply above.

I'm not sure that I've got any more general advice on how to approach these sort of problems, except for: do a lot of examples.  I must have done hundreds (thousands?) of these over the years!

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Thank you so much!

You tell me.

If you have 3 whole cakes and you eat 2/3 of one of them.

How many cakes are left?

4) Ball rolling down hill.

A ball rolling down a hill, in the absence of any significant friction or drag, is going to speed up, so the answer will be one with speed increasing.

The acceleration will result from the component of the gravitational force tangential to the surface of the hill.  Because the slope is decreasing as we move towards the bottom of the hill, this component is decreasing (when the ball is on the flat at the bottom of the hill, the tangential component of acceleration is zero, of course).

2) d:  Constant velocity must mean zero acceleration, so one cannot have constant velocity with changing (i.e. non-zero) acceleration.

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Take a look at this page I think that it will help.

Thank you Alan, that does help.  I can follow your logic without to much problem but I know that when I try to do it myself tomorrow I will not be able to.  You have explained things like this to me before and although i can follow your logic I do not seem to 'understand' it well it well enough to reproduce it on my own.  It is really frustrating. Do you have any suggestions  :(

Hi Alan and 315,

I am also trying to learn from these questions.

Question 2

I know that b and c are not possible but I am confused by a and d

Alan ( or 315) could you please discuss a and d ?

I am also struggling with the NEW question 4.

10/100*10816

the calc is on the home page :)

so all my answers are correct .. 

can you explain this for me 

Do you mean 1% pa compounding interest paid yearly for 7 years?

$$FV= 38000(1.01)^7$$

Yes, your answer is correct.

.

so my answer is correct or no  ? 

No, on second thoughts, I agree with your answer (I looked at this too quickly!)

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@@ End of Day Wrap           Thurs 23/10/14         Sydney, Australia           Time 9:00pm         ♬

Hi everyone,

Today our great answers were provided by Heureka, Rosala, Geno3141, CPhill, Bugzy3141, Fieldmoue830, Alan, Lostjr126, and Britishrain.    Thank you all.   

I sent an email to Andre Massow yesterday requesting some improvements to our message system and also improvements to access of the member data base.  I will keep you informed if I become aware of any changes.

Now for some interest posts:

1) Rosala is back in Camelot  Yeah!

why  .. ? 

Edited.  

See further reply below.

.

these are my answers :- 

1 - c 

2 - d 

3 - a 

4 - d 

5 - d 

are they correct ? 

e^x=2 what is x

$$\boxed{e^x = \ a^ { \dfrac{x}{\ln{(a)}} } = 2^ { \dfrac{x}{\ln{(2)}} }} \\ \\
e^x=2\\\\
2^ { \textcolor[rgb]{1,0,0}{\dfrac{x}{\ln{(2)}} } } } = 2^\textcolor[rgb]{1,0,0}{1} }\\\\
\textcolor[rgb]{1,0,0}{\dfrac{x}{\ln{(2)}} } } = \textcolor[rgb]{1,0,0}{1} \\\\
x=\ln{(2)}$$

That's correct!

.

It will be 8000cos65 to the left ! 

right  ?  

log(13x)=6.58   x=?

$$\small{\text{
$
\begin{array}{rcll}
\log_{10}(13x) &=& 6.58 & | \quad 10^{()} \\\\
13x &=& 10^{6.58} & | \quad :13 \\\\
x &=& \frac{10^{6.58}}{13}\\\\
x &=& 292453.381785
\end{array}
$
}}$$

Physics and chem questions that I want to get to:

(23/10/14)

The volume of a prism is area of cross section  x  height

so 

$$\\370=20\times h\\
$Divide both sides by 20$\\
h=370/20\\
h=18.5\;cm$$

Look at this.