Question

A metal washer 1 cm in diameter is pierced by a 1/2 cm hole. What is the area of one face of the washer?

Answer 1

ok, where you wwant to start is work out the area of the washer... before it had the hole cut in it
so it's just the equation for area of a circle, are u right with that?

Answer 2

Nope.

Answer 3

ok... area of a circle = pi x (radius)^2
your radius is half the length of the diameter (which was 1 cm)
so whats the area equal?

Answer 4

Pi/4

Answer 5

cool
now subtract the area of the hole from the area of the washer
Area of hole = pi x (radius squared)
radius of hole = 1/4 cm (given diameter of hole =1/2 cm

Answer 6

so what did you get for area of the hole?

Answer 7

pi/16

Answer 8

area = pi*r^2
= pi*(1/2)^2
= pi*1/4

next, calculate the center hole of diameter 1/2 area :-

area = pi*r^2
= pi*(1/4)^2
= pi*1/16

area of washer face = big circle area - hole area
= pi*1/4 - pi*1/16
= pi*4/16 - pi*1/16
= pi(4-1)/16
= 3pi/16

Answer 9

yep,
so pi/4 - pi/16 = area that's left
= 3pi/16 cm^2 or 0.1875 pi cm^2 or 0.589 cm^2

Answer 10

Aah, okay. Thank You :D

Answer 11

@Jack1 Two spheres of copper, of radii 1cm and 2 cm, respectively, are melted inside a cylinder of radius 1 cm. Find the altitude of the cylinder.

Answer 12

...altitude... height above the ground...?
what do you mean?
...how full is the cylinder in terms of height?

Answer 13

vol of sphere 1 = (4/3)*pi*1^3
vol of sphere 2 = (4/3)*pi*2^3
total volume of melted material = (4/3)*pi*9 ( sum of the above)
vol of the moulded cone = (1/3)*pi*r^2*h, where r = radius and h is height. Given r=1 So we have
(4/3)*pi*9 = (1/3)*pi*h; cancelling pi on both sides, we have
h = 36 cm

Answer 14

I dunno. It's just my assignment.

Answer 15

@Nurali you type quick ;D

Answer 16

But the choices are:
a. 2
b. 3
c. 4
d. 12