Engineering Q&A
A radioactive isotope has a half-life of 10 days. If today there are 125 g of it left, what was its original weight 40 days earlier 

(a) 600 g (b) 1000 g (c) 1250 g (d) 2000 g 
in Physics by

3 Answers

0 like 0 dislike
D. 2000g 

At the 40th day remaining isotope would be 125g

Since it's half life period is 10 days , on 30th day it would be double the 125g, i.e. 250g.

And on 20th day it would be double the 250g, i.e. 500g. And on 10th day it would be double the 500g i.e.1000g.

And before the radioactive decay the weight of isotope on the first Day will be double the 10th day, i.e. 2000g
by
0 like 0 dislike

2000g radio activ isotope have 10 day T1/2. So 40 days have a four T1/2 answer is 2000g.

 
by
0 like 0 dislike
Half life = 10days 

The formula which is, 1/(2)^n × original weight = Weight left today. 

To obtain the value of

n = divide no of days by half life

ie.,n= 40/10= 4

n=4

So, 1/(2)^n × original Weight = 125g

1/(2)^4 × Original weight = 125

Original weight = 16×125 = 2000g
by

Related questions

1 answer
2 answers
2 answers
Welcome to electronics2electrical.com, where students and teachers can ask and answer any question. Get help and answers to any engineering problem including Electrical, electronics, mechanical, telecommunication, instrumentation, computer, mathematics, physics etc. Get answers to questions. Help is always 100% free!

Most popular tags

power motor dc circuit transformer voltage current system used phase resistance factor ac load synchronous induction energy electric generator electrical series frequency capacitor between plant line speed transmission use meter type advantages difference single mosfet control function instrument problem magnetic amplifier high diode bjt machine unit source motors and diagram winding shunt field parallel define electricity torque value maximum time relay types arduino supply digital armature applications thyristor working transformers wave on flow operation three coil material instruments state ratio signal emf effect formula efficiency theorem method disadvantages starting microprocessor network test operating direction controlled different logic transistor single-phase scr loss temperature connected rc law force inductance compare measure station wire low conductor principle wattmeter full characteristics measuring constant measurement breaker losses device converter bridge linear materials nuclear matrix flux drive resistivity of machines angle switch free rectifier protection core circuits battery solar gain thermal loop generators open negative analog number lines friction reactance short gate pole inverter the conservation diesel iron resistors capacitance engineering basic using direct main electronic electronics a steam induced relays hysteresis universal transducer computer feedback range distribution work secondary igbt algebra pmmc plants factors capacitors dielectric controller regulation systems design air fault components rotor cable starter oscillator eddy alternator application semiconductor ammeter rl average forces damping rlc connection zener electromagnetic biasing minimum insulation pressure balanced permanent moving errors running copper self analysis impedance stability quality start ideal curve over commutation is 3-phase arc permeability peak bias error fuzzy commutator conductors superposition density mechanical rotation construction measured electrons charge memory inductive two transfer explain fuse methods off back three-phase tariff locomotive installation welding heating rms surge rating generation potentiometer coupled shaded rate capacity storage adc excitation active pure resistor harmonics reluctance microcontroller voltmeter inductor internal 8085 cro reaction insulating overhead hydro resonance traction definition breakers earth

9,196 questions

7,942 answers

156 comments

3,291 users

9,196 questions
7,942 answers
156 comments
3,291 users