Help with exponential growth and decay (1 Viewer)

[k150764]

hi i don't get this question..i tried it soo many times

The mass, in grams, of a radioactive substance is given by M=M0e^-kt
where t is time in years

find

b) mass after 15 years
c) rate of decay after 15 years

arent those the same question??
do u do something different?please help

 

[kaz1]

Rate means the value of dM/dt after 15 years.

 

[Aquawhite]

Where are the initial conditions or some information to work stuff out?

 

[addikaye03]

hi i don't get this question..i tried it soo many times

The mass, in grams, of a radioactive substance is given by M=M0e^-kt
where t is time in years

find

b) mass after 15 years
c) rate of decay after 15 years

arent those the same question??
do u do something different?please help

Theres not enough information for us to attempt the Q. But, they aren't the same thing.

Rate is dM/dt, ie. the change in M divided by the change is Time. Rate considers the values of M as it reaches 15 years and after 15 years ( if you get what i mean) to solve we must find dM/dt:

dM/dt=-k(Moe^-kt)

dM/dt=-kM

Then Sub in the info to find the Rate of change.

for b) is just asking for the instantaneous Mass (ie. the mass of the radioactive substance as it reaches 15 years old)

P.S: Please +ive rep me, i've got alot of neg lately lol