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Sphinxa [80]
3 years ago
12

the half life of a certain substance is 25 years. How long will it take for a sample of this substance to decay to 90% of its or

iginal amount ...?
Physics
1 answer:
Sveta_85 [38]3 years ago
3 0
10% =  1/2 ^n
*where n is number of half lives to reach 10%

n = ln10/ln2

and multiply by 25 gives 83.05 years to 2dp

Hope this helps
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Light is incident on an air-water interface at an angle of 30 degree to the normal. What angle does the refracted ray make with
Vikentia [17]

Answer:

22 degree

Explanation:

Angle of incidence, i = 30 degree

the refractive index of water with respect to air is 4/3.

As the ray of light travels from rarer medium to denser medium, that mean air to water, the refraction takes place.

According to Snell's law,

Refractive index of water with respect to air = Sin i / Sin r

Where, r be the angle of refraction

4 / 3 = Sin 30 / Sin r

0.75 = 2 Sin r

Sin r = 0.375

r = 22 degree

Thus, the angle of refraction is 22 degree.

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Which method of popcorn popping transfers heat into the kernels without any direct
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you plug in and turn on the popper, and then the hot air begins to rise in the popper while cooler air falls. As hot air circulates past the popcorn kernels and so the kernels absorb the hear

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Convert 3.45inches into km
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3 years ago
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A bar magnet was placed underneath a sheet of paper where a pile of iron filings sits. In the presence of the energy stored in t
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Answer: 1. The field energy will increase

2. The energy increases, and the lines of force are denser

3. It points toward the field of earths magnetic poles

4. 1 and 2 only

5. 2, 4, 1, 3

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2 years ago
A factory worker pushes a crate of mass 31.0 kg a distance of 4.35 m along a level floor at constant velocity by pushing horizon
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Answer:

a. 79.1 N

b. 344 J

c. 344 J

d. 0 J

e. 0 J

Explanation:

a. Since the crate has a constant velocity, its net force must be 0 according to Newton's 1st law. The push force F_p by the worker must be equal to the friction force F_f on the crate, which is the product of friction coefficient μ and normal force N:

Let g = 9.81 m/s2

F_p = F_f = \mu N = \mu mg = 0.26 * 31 * 9.81 = 79.1 N

b. The work is done on the crate by this force is the product of its force F_p and the distance traveled s = 4.35

W_p = F_ps = 79.1*4.35 = 344 J

c. The work is done on the crate by friction force is also the product of friction force and the distance traveled s = 4.35

W_f = F_fs = -79.1*4.35 = -344 J

This work is negative because the friction vector is in the opposite direction with the distance vector

d. As both the normal force and gravity are perpendicular to the distance vector, the work done by those forces is 0. In other words, these forces do not make any work.

e. The total work done on the crate would be sum of the work done by the pushing force and the work done by friction

W_p + W_f = 344 - 344 = 0 J

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3 years ago
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