# Thread: sugar dissolving

1. ## sugar dissolving

The mass M in grams of undissolved sugar left in a teacup after t seconds is given by: M=10.5-0.4t^2
When will all the sugar dissolve?
M=10.5-0.4t^2
-10.5=-0.4t^2
-10.5/-0.4=t^2
sqroot26.25=t
5.12s=t
can someone plz check if i did it right or can direct me in a right direction. Help would be appreciated.

2. You're solving for M=0. Your work looks right.

3. Originally Posted by crystal91
The mass M in grams of undissolved sugar left in a teacup after t seconds is given by: M=10.5-0.4t^2
When will all the sugar dissolve?
M=10.5-0.4t^2
-10.5=-0.4t^2
-10.5/-0.4=t^2
sqroot26.25=t
5.12s=t
can someone plz check if i did it right or can direct me in a right direction. Help would be appreciated.
If t= 5.12 then M= 10.5- 0.4(5.12)^2= 10.6- 0.4(26.2144)= 10.5- 10.48576=0.01424 so your answer is approximately correct. It might be better to leave the answer as $t= \sqrt{26.25}$ or $t= \frac{\sqrt{105}}{2}$.