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tiny-mole [99]
3 years ago
6

Calcium-51 has a half-life of 4.5 days. Only 0.75 gram remains of a sample that was initially 12 grams. How old is the sample of

calcium-51?
Physics
2 answers:
Over [174]3 years ago
6 0
How many times did the original sample lose 50% of its radioactivity ?

-- Start with. . . . . . . . . . . . 12 grams.
-- Lose half of it once. . . . . . 6 grams left.
-- Lose half of it again . . . . . 3 grams left.
-- Lose half of it again . . . . . 1.5 grams left.
-- Lose half of it again . . . . . 0.75 gram left.

-- How many times did it lose half ?    4 times.

-- How long does it take to lose half ?  4.5 days. 
                                                       (That's why it's called the 'half-life'.)

-- How long did it take to lose half, 4 times ?

                                           (4 x 4.5 days) = 18 days .
tatiyna3 years ago
3 0

Answer:

18 days

Explanation:

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A sort of "projectile launcher" is shown below. A large current moves in a closed loop composed of fixed rails, a power supply,
Zarrin [17]

Answer:

wallah i don't understand anything with my stoopid brain

Explanation:

3 0
2 years ago
A circular sign has a diameter of 40 cm and is subjected to normal winds up to 150 km/h at 10°C and 100 kPa. Determine the drag
Marat540 [252]

Answer:

147.7 N

221.55 Nm

Explanation:

P = Pressure = 100000 Pa

R_s = Mass-specific gas constant = 287.015 J/kg k

T = Temperature = 10+273 = 283 K

C = Drag coefficient = 1.1

A = Area

r = Radius = 0.2 m

v = Speed of wind = \frac{150}{3.6}\ m/s

L = Length of pole

Density

\rho=\frac{P}{R_sT}\\\Rightarrow \rho=\frac{100000}{287.058\times 283}\\\Rightarrow \rho=1.2309\ kg/m^3

Drag force

F=\frac{1}{2}\rho CAv^2\\\Rightarrow F=\frac{1}{2}\times 1.2309\times 1.1\times \left(\pi \times 0.2^2\right)\times \left(\frac{150}{3.6}\right)^2\\\Rightarrow F=147.7\ N

Force on the circular sign is 147.7 N

M=F\times L\\\Rightarrow M=147.7\times 1.5\\\Rightarrow M=221.55\ Nm

Bending moment at the bottom of the pole is 221.55 Nm

6 0
3 years ago
How long does it take to change a flat plain into mountains? help
Len [333]
Im not for sure but i think it takes a couple hundred years (or according to the climate)
5 0
3 years ago
Read 2 more answers
Which statement accurately describes current electricity?
ludmilkaskok [199]
Current electricity is caused by flowing negatively charged particles.
5 0
1 year ago
What is number 30,31 in this picture?
Maslowich
On question 30, that is a displacement- time graph (DT). On this type of graph the gradient is equal to the velocity. B has the steepest gradient, then A and finally C

Now velocity is a vector quantity so it has a direction and speed ( speed doesn't have a fixed direction.)

on the DT graph im going to assume that movement B is a positive velocity with A and C being negative. 
So by ranking these: A is the most negative, C is the least negative and B has to be the greatest as it is the only positive velocity. 

Q31, The same type of graph is present, by looking at the gradients we can rank the largest and smallest velocities- speeds in the case of the question. 
i'll skip my working out as its the same as before:

C, B, A and then D

the same idea as on Q30 applies to Q31 part b, 

D,C,B then A 
6 0
3 years ago
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