Rachel has an unknown sample of a radioisotope listed in the table. Using a special technique, she is able to measure the mass of just the unknown isotope as 104.8 kg at 12:02:00 P.M. At 4:11:00 P.M. on the same day, the mass of the unknown radioisotope is 13.1 kg. Which radioisotope is in the sample?


Answer 1




initial mass of the sample at 12:02:00 PM is given as

Mass of the sample at 4:11:00 PM is given as

so here since it is a sample of radioactive isotope so here we will say

now from above data we know that the time taken to reduce the mass is

now from above equation we will have

so here half life is given as

So here this isotope must be the one which will have half life of 1.4 hours

So it is nearly Barium-139

Answer 2
Answer: Barium-139 is the correct answer.

Related Questions


Define one second Define one kg mass. Define one solar day ​


One second- One second is the time that elapses during 9,192,631,770 (9.192631770 x 10 to the 9th power ) cycles of the radiation produced by the transition between two levels of the cesium 133 atom.

One kg mass- the mass of a particular international prototype made of platinum-iridium and kept at the International Bureau of Weights and Measures. It was originally defined as the mass of one liter (10^-3 cubic meter) of pure water. At the Earth's surface, a mass of 1 kg weighs approximately 2.20 pounds (lb)

One solar day- the time between successive meridian transits of the sun at a particular place





Objects with masses of 191 kg and 572 kg are separated by 0.406 m. A 50 kg mass is placed midway between them. 0.406 m b b 191 kg 50 kg 572 kg Find the magnitude of the net gravitational force exerted by the two larger masses on the 50 kg mass. The value of the universal gravitational constant is 6.672 × 10−11 N · m2 /kg2 . Answer in units of N.



3.06 x 10^{-5} N


mass M1 = 191 kg

mass M2 = 572 kg

mass M3 = 50 kg

distance apart (d) = 0.406 m

gravitational constant (G) = 6.62 x 10^{-11} m^{2}/kg^{2}

Find the magnitude of the net gravitational force exerted by the two larger masses on the 50 kg mas

the net  gravitational force acting on the 50 kg mass (M3) = gravitational force exerted by the larger mass (M2) - gravitational force exerted by the smaller mass (M1)

  • y = distance between masses M2 and M3 = 0.406/2 = 0.203
  • y1 = distance between masses M1 and M3 = 0.406/2 = 0.203
  • y = y1 = 0.203

net force =

net force =

net force =  

net force = 3.06 x 10^{-5} N


Does the air in a balloon have masd


I'm not sure what 'masd' is, but I can assure you that air has 'mass', and it has weight too.

A heat engine operates between 35 C and 330 C. If this engine extracts a total energy of 800 MJ from fuel, then how many MJ of energy could be used as useful mechanical energy? Remember that e = 1 - T(low)/T(high), where T is in Kelvin (= Celsius + 273).



Machine used 392 MJ energy as mechanical energy.


Efficiency(e) is defined as the ratio of the work done by the machine to the energy provided to the machine.


The efficiency of the machine is also given by the relation :


Here T(low) and T(high) denotes the temperature in kelvin.

According to the problem, T(low) = 35⁰ C = 35 + 273 = 308 K

                                            T(high) = 330⁰ C = 330 +273 = 603 K

Substitute the values of T(low) and T(high) in the equation (2).

e = 0.49

According to the problem, Energy Given = 800 MJ

Substitute the value of efficiency(e) and Energy Given in the equation (1).

Energy used = 0.49 x 800 MJ = 392 MJ

Random Questions