6.There are four mixtures A, B, C and D. The mixture A contains sand and sugar, mixture B contain chalk powder and salt, mixture C contains salt and sugar, whereas mixture D contains sugar and charcoal powder. Which one of these mixtures cannot be separated by using water as a solvent? Why?

Two red blood cells each have a mass of 9.0 multiply. gif 10-14 kg and carry a negative charge spread uniformly over their surfaces. the repulsion arising from the excess charge prevents the cells from clumping together. one cell carries −2.50 pc of charge and the other −3.10 pc, and each cell can be modeled as a sphere 7.5 μm in diameter. (a) what speed would they need when very far away from each other to get close enough to just touch? assume that there is no viscous drag from any of the surrounding liquid. answer is: 321 m/s how do i find this (b) what is the maximum acceleration of the cells in part (a)? answer is: 1.38e+10 m/s2 how did they find this answer

Given the position vector of the particle r(t)=(t+1)i+(t^2−1)j+2t k, find the particle's velocity and acceleration vectors at t=1

This is for my 8th grade science class, i really don’t understand. can someone me? , lol.