physics
posted by usha
An empty plastic box of mass 9 kg is found to accelerate up at the rate of g/3 m/sec2 when placed deep inside water. Mass of the sand that should be put inside the box so that it may accelerate down at the rate of g/4 m/sec2 is

bobpursley
Lets do this the long way.
In the water, the net force=mass*acceleration (neglecting considerable friction).
but net force=bouyantforcemg or
bouyant force=mass*g* 1/3 +mg=4/3 mg
this bouyant force does not change. So to go now,
bouyant force(m+Masssand)g=1/4 (M+m)
4/3 mgmgMg=1/4 mg
Mg=mg(.25+1.33)
solve for M
check all this.
Respond to this Question
Similar Questions

math
it is cross math (like sudouk) six rows across and six rows down 1st row has empty box, +, empty box, + box =6 this row is across 2nd row has x blacked out box, +, blacked out box, x, blacked out box this row is across 3rd row across … 
physics
1) Two boxes are placed are placed side by side on a frictionless surface so that they touch each other. Box A has a mass of 4 kg. Box B has a mass of 12 kg. A constant force of 24 N is applied to box A. What force does box A exert … 
Physics
A block of mass m is attached to a string and suspended inside an otherwise empty box of mass M. The box rests on a scale that measures the systemâ€™s weight. (a) If the string breaks, does the reading on the scale change? 
physics
Suppose that a 1.00 cm3 box in the shape of a cube is perfectly evacuated, except for a single particle of mass 1.13 x 10^3 g. The particle is initially moving perpendicular to one of the walls of the box at a speed of 525 m/s. Assume … 
physics
A force of 99 N causes a box to accelerate at a rate of 11 m/s2. What is the mass of the box? 
Math
I think this is geometry: There is a small box with a black frame around it. Inside the box, at the bottom, is an 8. Inside the box, to the right, is a 2. It looks like they are showing Length & Height. On the outside of the box, under … 
Math
Danny needs to buy sand for this box. He wants to nearly fill the box leaving only 6 inches empty at the top. How much sand does Danny need if the length is 12 feet the width is 2 feet and the height is 3 feet. I first found the volume … 
physics
A box is put on a scale that is marked in units of mass and adjusted to read zero when the box is empty. A stream of marbles is then poured into the box from a height h = 6.93 m above its bottom at a rate of R = 128 (marbles per second). … 
Physics
A cubical metal box has side L=10.34cm and mass m=150 g. How much mass must be placed inside the box if it is to float in water with its top at the surface? 
science
A crane accidently drops a box full of material into a freshwater pool measuring 20 feet long, 10 feet wide, and 6 feet deep before the box is dropped causing the water level to rise to 6.05 feet after the box is dropped. The box is …