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garik1379 [7]
3 years ago
13

A radioactive substance decays according to the formula w = 20e¡kt grams where t is the time in hours. a find k given that after

50 hours the weight is 10 grams. b find the weight of radioactive substance present at: i t = 0 hours ii t = 24 hours iii t = 1 week. c how long will it take for the weight to reach 1 gram? d find the rate of radioactive decay at: i t = 100 hours ii t = 1000 hours. e show that dw dt is proportional to the weight of substance remaining.
Physics
1 answer:
blagie [28]3 years ago
5 0
W=20 e(-kt)  
A. Rearranging gives k= -(ln(w/20)/t 
 Substituting w= 10 and solving gives k=0.014 
 B. Using W=20e(-kt). After 0 hours, W=20. After 24 hours, W=14.29g. After 1 week (24x7=168h) W=1.9g 
 C. Rearranging gives t=-(ln(10/20)/k. Substituting w=1 and solving gives t=214 hours. 
 D. Differentiating gives dW/ dt = -20ke(-kt). Solving for t=100 gives dW/dt = 0.07g/h. Solving for t=1000 gives 0.0000002g/h 
 E. dW/dt = -20ke(-kt). But W=20e(-kt) so dW/dt = -kW
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Answer:

L = 1.11 x 10^{6} m, is the length of piece of 20 cm wide Aluminum foil to make capacitor large enough to hold 52000 J of energy.

Explanation:

Solution:

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Dielectric Constant of the plastic Bag = 3.7 = K

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