T = half life period of decay for atoms of element A = 20,000 years
N₀ = initial number of atoms of element A = 10,000 atoms
N = final number of atoms after time "t" = 2500 atoms
t = time of decay = ?
λ = decay constant = ?
decay constant is given as
λ = 0.693/T
λ = 0.693/20,000
λ = 0.00003465 years⁻¹
atoms after decay for time "t" is given as
N = N₀ 
inserting the values
2500 = (10000) 
t = 40,000 years
so correct choice is
B) 40,000 years
<span>The weightlifter does no work. Although he has exerted force, work is the product of force over distance. Since he has not moved the wall he has done no work.</span>
Answer:
<u>Range</u><u> </u><u>is</u><u> </u><u>6</u><u>2</u><u>.</u><u>5</u><u> </u><u>metres</u>
Explanation:
Time of flight

for range, acceleration is zero
from second newton's equation:

but a = 0:
let range be x:

[ taken g to be 10 m/s² ]
Answer:
Whenever you see the delta symbol infront of another, it always represents change. In other words:
Δu = u_f - u_i
- u_i means "initial velocity"
- u_f means "final velocity"
And in general, ΔX means Xfinal - Xinitial