Via half-life equation we have:

Where the initial amount is 50 grams, half-life is 4 minutes, and time elapsed is 12 minutes. By plugging those values in we get:

There is 6.25 grams left of Ra-229 after 12 minutes.
The answer is 0.025J.
W=1/2*k*x^2
W=1/2*20*0.050^2
W=0.025J
Answer:
0.976 c
Explanation:
= velocity of object 1 relative to earth = 0.80 c
= velocity of object 2 relative to object 1 = 0.80 c
= velocity of object 2 relative to earth
Velocity of object 2 relative to earth is given as


= 0.976 c
Work is force times distance, so W = 40 N * 10 m = 400 J
speed of the striking object is given as

now this speed in SI units given as


So here we can use kinematic now to find the height from where it is dropped
so here we will have

now we have



now from above equation


now we know that average height of 1 story building is 3 meter
so approx total number of stories in the building will be
