Which has more mass, a kilogram of feathers or a kilogram of iron?

An insulated thermos contains 148 g of water at 72.7 ˚c. you put in a 11.7 g ice cube at 0.00 ˚c to form a system of ice + original water. the specific heat of liquid water is 4190 j/kg•k; and the heat of fusion of water is 333 kj/kg. what is the net entropy change of the system from then until the system reaches the final (equilibrium) temperature?

Which of the the following are examples of projectile motion of both projectile motion and two dimensional motion

How to know which equation of motion to use where?explain