Calculate the energy needed to heat 4 kg of water from 25 degrees c to 45 degrees c

Students design a model roller-coaster track. they place a rubber ball at the highest point on the track and let it go. the ball rolls along the track pulled only by the force of gravity. eventually, it comes to a stop. which change to the design will result in the ball moving the greatest distance?

If forces acting on an object are unbalanced. true or false

What is the coefficient of kinetic friction μk between the block and the tabletop?