A person trying to lose weight (dieter) lifts a 10 kg mass, one thousand times, to a height of 0.5 m each time. Assume that the potential energy lost each time she lowers the massis dissipated:- Fat supplies `3.8 xx 10^7J` of energy per kilogram which is converted to mechanical energy with a 20% efficiency rate. How much fat will the dieter use up?

A person trying to lose weight (dieter) lifts a 10 kg mass, one thousand times, to a height of 0.5 m each time. Assume that the potential energy lost each time she lowers the massis dissipated:- How much work does she do against thegravitational force ?

An alpha particle (_2He^4) is moving directly towards a stationary gold nucleus (_(79)Au^(197)) .The alpha -particle and the gold nucleus may be considered to be solid spheres with the charge and mass concentrated at the centre of each sphere.When the two spheres are just toching,the sepaation of their centres is 9.6 xx 10^(-15) m . the alpha particle and the gold nucleus may be assumed to be an isolatedd system.Calculate for the alpha particle just in contact with the gold nucleus, its electric potential energy.

A person of mass 60 kg wants to lose 5 kg by going up and down a 10 m high stairs. Assume he burns twice as much fat while going up than coming down. If 1 kg of fat is burnt on expending 7000 kilo calories, how many times must he go up and down to reduce his weight by 5 kg?

Suppose the average mass of raindrops is 3.0 xx 10^-5 kg and their average terminal velocity 9 ms^-1 . Calculate hte energy transferred by rain to each square metre of the surface at a place which receives 100 cm of rain in a year.

On complete combustion a litre of petrol gives off heat equivalent to 3 xx 10^7 J . In a test drive a car weighing 1200 kg, including the mass of driver, runs 15 km per litre while moving with a uniform speed on a straight track. Assuming tha friction offered by the road surface and air to be uniform, calcuate the force of friciton acting on the car during the test drive, if the efficiency of the car engine were 0.5.

One end of a long string of linear mass density 8.0 xx 10^-3 kg m^-1 is connected to an electrically driven tuning fork of frequency 256 Hz. The other end passes over a pulley and is tied to a pan containing a mass of 90 kg. The pulley end absorbs all the incoming energy so that reflected waves at this end have negligible amplitude. At t= 0, the left end (fork end) of the string x = 0 has zero transverse displacement (y = 0) and is moving along positive y-direction. The amplitude of the wave is 5.0 cm. Write down the transverse displacement y asfunction of x and tthat describes the wave on the string

In a photoelectric effect set up, a point source of light of power 3.2 xx10^(-3) W emits monoenergetic photons of energy 5eV.The source is located at a distance of a stationary metallic sphere of work function 3eV and radius 8xx10^(-3)m .The efficiency of photoelectron emission is one for every 10^(6) incident photons.Assume that the sphere is isolated and initially neutral and the photoelectrons are initially swept away after emission. Calculate the number of photoelectrons emitted per second.

Surface tension is exhibited by liquids due to force of attraction between molecules of the liquid. The surface tension decreases with increase in temperature and vanishes at boiling point. Given that the latent heat of vaporation for water rho_(w) = 540kcal/kg ,mechanical equivalent heat =4.2j/cal Avogadro's No. N_A = 6.0 xx 10^26 , and the molecular weight of water M_A = 18 kg for 1 k mole. Estimate the energy required for oe molecule of water to evaporate.