Question

1.What is the unit for kinetic energy?

2.A collision in which kinetic energy is conserved is called what?

3. It takes no work to hold a cheerleader in the air, as shown here. If no work is done by the cheerleaders, why do they eventually tire?

	A.The concept of work, as it apples in physics, does not apply to any process that involves people.
	B.Their bodies expend chemical energy as their muscles function; this is "hard work," but not the same kind of work that moves a mass over a distance.
	C.The arrangement is unstable and they can easily fall over.
	D.The cheerleaders at the greater height have more potential energy.
	E. Maintaining the same position for a long time is boring. 4.If the orbit is elliptical, rather than circular, what can be said about the work done by the Sun on Earth? a.If the orbit is elliptical, work is done to speed up or to slow down Earth, depending on its location in orbit. b.Whether the orbit is circular or elliptical, work must be done to propel Earth around the Sun.   c The work the Sun does on Earth causes the tides. d.The work the Sun does on Earth accounts for Earth's changes of season. E. It does not matter whether the orbit is circular or elliptical, no work is done. 5.In a rollercoaster, provided losses of thermal energy because of friction can be neglected, which of the following is true? A.The kinetic energy decreases as the car moves to the top of the slope. B.The rollercoaster moves at constant speed as its height above the ground increases.     C. The gravitational potential energy decreases as the car moves to the top of the slope. D.The mechanical energy decreases as the car moves to the top of the slope. E.The mechanical energy increases as the car moves to the top of the slope.

Answer 1

1)SI unit of kinetic energy is joule .It can be denoted as 'J'

2) A collision in which kinetic energy is conserved is called elastic collision .

3) holding any thing in air doesn't mean the work done happen. Because to do work done we need force as well as displacement . Holding cheerleader in air in this process we apply reaction force in opposite to the gravity but there is no displacement hence no work done or work done=0 J

In ideal case they never be get tired but in practical case their body expands chemically and muscles functions this done hard work but not the same kind of work which moves the object over distance .Due to this their body blood pressure is changes and blood has their own mass and it as force as well and simultaneously it's runs throughout the body hence boold molecules does the work here and that's why person feels tired.

4) if orbit is elliptical rather than circular that the work done by the sun on the earth ea changes becaibe in elliptical orbit force between the earth and the sun is changes at every position but momentum maintaining constant.