Aforce of 6n is exerted on a cart that is carrying a rock and produces an acceleration of 2 m/s2. if the cart has a mass of 1 kg, what is the mass of the rock?

If you use the equation F=ma and re-arrange it to get m = F/a, you'll get the total mass. Then you have to subtract the mass of the cart from the total mass to get the mass of the rock. 

Thus, m = 6N over 2m/s^2. The total mass will then be 3kg. Subtracting 1kg from the total mass will then yield you 2kg, which is the mass of the rock. Hope this helps.

A. they hold atoms  together with a molecule.its a force that exist between molecules. hope this .