# modern physics...

#### physics21

plz help!(Sweating)

Q). A certain strain of bacteria doubles in number each 20 days. Two of these bacteria are placed on a spaceship and send away from earth for 1000 earth days. During this time the speed of the ship was 0.9950 c. How many bacteria would be aboard when the ship lands on the earth?

the answer given is 64 .

#### physics21

how is the speed of spaceship related to the doubling time of bacteria in the above question?

one more doubt i have....

Q). A dust particle of mass 0.01g is enclosed in a cubical box of side 1 cm. The lowest energy (J) associated with the particle will be?(h=6.62 x 10^-27 erg s)

can it be solved as....

energy= hc/lambda , where lambda could be taken as 1 cm?? if this is the way it should be....what is the use of MASS of the particle??

plz tell me if i am going right because the answer has not been provided in the book

thank you

Last edited:

#### Haytham

the first question is about relativistic time dilation

as the ship is moving close to the speed of light, time psasses slower in the ship than on earth

you need to figure out how much time has passed in the ship if on earth passed 1000 days

you should use
t'=t/sqrt(1-v²/c²)

physics21

#### physics21

Thank you Haytham! (Clapping)