(1) a cone has a base radius of 7cm and slant height of 5cm. calculate the surface area of the cone, in cm^2, correct to 3 significant figures.

(2) the density of mercury is 13.6g cm^-3. find the mass of 4.7-10^-5cm^3 mercury. give your answer correct to 2 significant fugures.

Question

(1) a cone has a base radius of 7cm and slant height of 5cm. calculate the surface area of the cone, in cm^2, correct to 3 significant figures.

(2) the density of mercury is 13.6g cm^-3. find the mass of 4.7-10^-5cm^3 mercury. give your answer correct to 2 significant fugures.

anonymous · Answer

what equation do you have for the surface area of a cone ?

and what is the equation for density if you recall?

anonymous · Answer

i ues the formula to find the answer but that answer was wrong .. (first question)

anonymous · Answer

|dw:1357721242644:dw|

anonymous · Answer

the $$\pi3.142$$

anonymous · Answer

Here, r is the radius, s is the slant height, and h is the altitude (height).

We can use Pythagorean's Theorem is calculate the height.  Then use the equation

$$S = \pi r \sqrt{r^{2} + h^{2}}$$

to determine the surface area

anonymous · Answer

Are you sure the problem says the slant height is 5 cm and the radius is 7 cm?  That would be impossible.

anonymous · Answer

i'm sure ..  i copy from book

anonymous · Answer

Sure it isn't the other way around?

If the radius is 7 cm then the slant height would have to be more than 7 cm, not less than it.

anonymous · Answer

the answer of the first question is $$2.64\times10^{-2}cm ^{2}$$

anonymous · Answer

but i don't know how to do..

anonymous · Answer

The slant height is 5 cm?  Not 50 cm?  Not 15 cm?

We cannot have a slant height that is smaller than the radius of the cone.  There is no such geometric object.

anonymous · Answer

no