Aroller coaster car (mass = m) is on a track that forms a circular loop (radius = r) in the vertical plane. if the car is to just maintain contact with the track at the top of the loop, what is the minimum value for its speed at that point?

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

Which planet do you think would be easiest for humans to colonize some day?

If a star is moving toward earth, it is