Achild rides a merry-go-around while turning with uniform circular motion. at time t 2 s, the child's velocity is vi = (4.5 m/s)î+ (4 m/s)j, measured on a horizontal xy coordinate system. at time t2 7s, a half-revolution later, the child's velocity is v(-4.5 m/s)î + (-4 m/s)j (a) what is the magnitude of the child's average acceleration during the time interval t2-t? (b) what is the child's centripetal acceleration (magnitude of the child's radial acceleration) during the time interval t2 t? (c) what is the child's radial acceleration vector (using î andj) at t2? at time t2, the merry-go-round begins to slow down, coming to a complete stop just as it completes two full rotations after t2- during this time, the child experiences a constant tangential acceleration. (d) what is the magnitude of the child's tangential acceleration during the time it takes the merry-go-round to come to a complete stop?

Energy transformations are processes that convert energy from one type (e.g., kinetic, gravitational potential, chemical energy) into another. any type of energy use must involve some sort of energy transformation.energy must obey the laws of thermodynamics.thermodynamics is the study of how energy changes from one type to another. the laws of thermodynamics apply to energy and energy conversions.the first law of thermodynamics: main articleenergy cannot be created or destroyed (which is called the conservation of energy); however, it can be transformed from one type into another. in fact, every useful process transforms energy from one form to another. there are many different forms or types of energy. some examples of everyday energy transformations are: scenario energy conversions involvedrubbing hands together to make them warm kinetic energy to thermal energyusing a battery-powered flashlight chemical energy to electrical energy (in the battery)electrical energy to radiant energy (in the bulb)an object speeding up as it falls gravitational potential energy to kinetic energythe second law of thermodynamics: main articlesome forms of energy are more useful than others. using energy always makes it less useful, even though no energy is actually destroyed.kinetic energy and electricity are the most useful forms. these are "high-quality" because they can be transformed almost completely into any other type of energy. electricity, for example, can be easily used to generate heat (thermal energy) or light (radiant energy), break chemical bonds (chemical energy), move objects (kinetic energy), or lift objects (gravitational potential energy).the least useful form of energy is low-temperature thermal energy. it can still be converted back to a higher-quality form, but useful energy is always lost in this process. converting energy to a less-useful form and then trying to work backwards never gets 100% of the useful energy back.for example, when a car runs, the engine will become hot (thermal energy). the warmth of the engine does nothing to the car move or go faster. this wasted energy is an unavoidable by-product of converting the car's fuel (chemical energy) into movement ("high-quality" kinetic energy), however it can potentially be used for heating the cabin of the car to slightly increase overall energy efficiency. it is a challenge for all forms of power generation to minimize wasted energy and be as efficient as possible.

When someone eats food