Answer: 
Explanation:
Given
Radioactive material is found to decrease 40% of its original value in 
Sample at any time is given by

where, 
Put values

Taking natural logarithm both side

The correct answer is #4. They have the same number of protons but a different number of neutrons.
Chemical Potential Energy is released when chemical bonds between atoms are broken (like covalent and ionic) and is released mainly as thermal
<span>Elastic Potential is released when the molecules in the material are allowed to go back to there original form, and is released mainly as kinetic</span>
Answer: In young's double slit experiment that uses monochromatic light the interference pattern formed has Central bright band with alternate dark and bright band That is option B.
Explanation: In this young experiment two small slits Namely a and b are formed on the screen and a monochromatic light is focused on them. Wavelets come out of of this lets scintillating and overlapping each other. This we get from huyginns principal, thus forming alternate dark and bright bands with bright band at center and all bands are about one meter apart.
Answer:
7km
Explanation:
The angle of depression is congruent to the angle of elevation and can be explained as angle below horizontal in which the person observing an object must view for him/her to view object's that are lower than him/her.
In angle of depression, there is assumption that object is closer to the person observing it, so there is parallel horizontal for both observing and object been observed.
hot air balloon 2 km high,
there exist two triangles
From trigonometry
Tanx= opposite/adjacent
Opp= 2km
Adj= X1
first triangle have base length of
Tan(16)=2/X1
X1=2/ tan(16)
X1=6.97
For Second triangle
Tanx= opposite/adjacent
Opp= 2km
Adj= X2
the other with a base length of
X2=2/tan(84)
X2=0.21
Therefore,, the total distance between the two towns is
x1+x2=6.97+0.21=7.18km