Answer:
160 years.
Explanation:
From the question given above, the following data were obtained:
Initial count rate (Cᵢ) = 400 count/min
Half-life (t½) = 40 years
Final count rate (Cբ) = 25 count/min
Time (t) =?
Next, we shall determine the number of half-lives that has elapse. This can be obtained as follow:
Initial count rate (Cᵢ) = 400 count/min
Final count rate (Cբ) = 25 count/min
Number of half-lives (n) =?
Cբ = 1/2ⁿ × Cᵢ
25 = 1/2ⁿ × 400
Cross multiply
25 × 2ⁿ = 400
Divide both side by 25
2ⁿ = 400/25
2ⁿ = 16
Express 16 in index form with 2 as the base
2ⁿ = 2⁴
n = 4
Thus, 4 half-lives has elapsed.
Finally, we shall determine the time taken for the radioactive material to decay to the rate of 25 counts per minute. This can be obtained as follow:
Half-life (t½) = 40 years
Number of half-lives (n) = 4
Time (t) =?
n = t / t½
4 = t / 40
Cross multiply
t = 4 × 40
t = 160 years.
Thus, it will take 160 years for the radioactive material to decay to the rate of 25 counts per minute.
Answer:
When did humans learn that the Earth is not the center of the universe?
Answer
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4 Answers
Asked in 3 Spaces


Science - Next Generation
Alexander Somm
, Consultant, Investor Relations at Novelpharm AG (2015-present)
Answered Oct 16
What, it isn’t?!
Sorry, I had to.
As far as I have read and understood, the Sumerians and later the Babylonians both had astronomical calendars that already differentiated planets and stars. Earth was not the center to them, the Sun likely was. That was around 2,200 - 1,600 BC.
After that, Greek philosopher Aristarchus of Samos (310 - 230 BC) was the first (recorded) to have believed the solar system was organized around the Sun, rather than the Earth. His heliocentric model was unpopular during Aristarchus’ lifetime, although it would inspire astronomers centuries later, such as Copernicus and Galileo.
Now, there are numerous archeological findings (cave paintings) and studies, that all suggest an understanding of complex astronomy in prehistoric times dating back as far as 40,000 years. This also explains how early, prehistoric migrants may have navigated the seas.
Explanation:
hope it helps
have a good day
Answer:
a) 19440 km/h²
b) 10 sec
Explanation:
v₀ = initial velocity of the car = 45 km/h
v = final velocity achieved by the car = 99 km/h
d = distance traveled by the car while accelerating = 0.2 km
a = acceleration of the car
Using the kinematics equation
v² = v₀² + 2 a d
99² = 45² + 2 a (0.2)
a = 19440 km/h²
b)
t = time required to reach the final velocity
Using the kinematics equation
v = v₀ + a t
99 = 45 + (19440) t
t = 0.00278 h
t = 0.00278 x 3600 sec
t = 10 sec
Answer: Gravity
Explanation: Gravity is pulling down on the ball, making it stay on the floor
.
. The input force is analogous or equivalent to the effort applied i.e.
.