# calculus

posted by .

can someone check these for me:

18. All edges of a cube are expanding at a rate of 6 cm per second. How fast is the volume changing when each edge is a) 2 cm and b) 10 cm.

a)72 cm^3/sec b)1800 cm^3/sec

20. The formula for the volume of a cone is v=(1/3)(pi)(r^2)h. Find the rates of change of the volume if dr/dt is 2 in per min and h=3r when a) r=6 in and b)r=24 in

a)216(pi) in^2/min
b)12864(pi) in^2/sec

thanks

• calculus -

18. correct
20 a) correct
b) I got 3456π inches^2/min (why have you got in^2/sec ? )

## Similar Questions

1. ### MATH!

If the edge of a cube is increased by 50%, then the volume is increased by x%. Find x. PLEASE HELP. THANK YOU. Let Y = edge of a cube. Y + 0.5Y = 1.5Y = new edge of the cube. Then old volume is Y^3 New volume is (1.5Y)^3 = 2.375Y^3. …
2. ### 12th Calculus

the volume of a cube is increasing at the rate of 1200 cm^3/min at the instant it edges are 20cm long. at what rate are the edges changing at the instant?
3. ### Calculus

The edge of a cube is increasing at a rate of 2 inches per minute. At the instant when the volume is 27 cubic inches, how fast is the volume changing?
4. ### calculus

the side of a cube is expanding at a constant rate of 2 centimeters per sesond. what is the instantaneous rate of change of the surface area of the cube, in cm2 per second, when its volume is 27 cubic cm
5. ### calculus

the edge of a cube is increasing at the rate of .05 centimeters per second. in terms of the side of the cube s, what is the rate of change of the volume of the cube, in cm^3/sec
6. ### calculus

All wedges of a cube are expanding at a rate of 6 cm/sec .How fast is the surface area changing when each edge is (a) 2 cm and (b) 10cm
7. ### calculus

All wedges of a cube are expanding at a rate of 6 cm/sec .How fast is the surface area changing when each edge is (a) 2 cm and (b) 10cm
8. ### calculus

the edges of a cube are increasing at the rate of 5 in/min. How fast is the volume changing when each side is 4 in.
9. ### Calculus

All edges of a cube are expanding at the rate of 3 centimeters per second. How fast is the volume changĀ­ ing when each edge is (a) 1 centimeter and (b) 10 centimeters?
10. ### Calculus

All edges of a cube are expanding at a rate of 8 centimeters per second. (a) How fast is the volume changing when each edge is 4 cm?

More Similar Questions