Question

An hourglass consists of two sets of congruent composite figures on either end. Each composite figure is made up of a cone and a cylinder.


© 2011 Jupiterimages Corporation

Each cone of the hourglass has a height of 18 millimeters. The total height of the sand within the top portion of the hourglass is 54 millimeters. The radius of both cylinder and cone is 8 millimeters. Sand drips from the top of the hourglass to the bottom at a rate of 10π cubic millimeters per second. How many seconds will it take until all of the sand has dripped to the bottom of the hourglass?

Answer 1

68.3

38.4

268.8

230.4

Answer 2

ok - so you need to find the volume of the sand in the top of hourglass
= vol in cylinder + vol in cone
vol in cylinder = pi r^2 h
where r - 8 and h = 54-18 = 36

vol in cone = (1/3) pi r^2 h
where r=8 and h = 18

add these 2 together to find the total volume

then time taken = total volume / rate of flow

Answer 3

leave the results in terms of pi
for example vol of cylinder = pi * 8^2 * 36 = 2304 pi cm^3

do you follow this ok?

Answer 4

yes i understand this now! thank you soo much :)

Answer 5

when you do final calculation the pi's will cancel out

Answer 6

yw