Answer: 86.47 g of carbon-14 must have been present in the sample 11,430 years ago.
Explanation:
Half-life of sample of carbon -14= 5,730 days
Let the sample present 11,430 years(t) ago = 
Sample left till today ,N= 0.060 g
![ln[N]=ln[N]_o-\lambda t](https://tex.z-dn.net/?f=ln%5BN%5D%3Dln%5BN%5D_o-%5Clambda%20t)
![\log[0.060 g]=\log[N_o]-2.303\times 0.00012 day^{-1}\times 11,430 days](https://tex.z-dn.net/?f=%5Clog%5B0.060%20g%5D%3D%5Clog%5BN_o%5D-2.303%5Ctimes%200.00012%20day%5E%7B-1%7D%5Ctimes%2011%2C430%20days)
![\log[N_o]=1.9369](https://tex.z-dn.net/?f=%5Clog%5BN_o%5D%3D1.9369)
86.47 g of carbon-14 must have been present in the sample 11,430 years ago.
Answer: copper
Explanation: when a spoon is placed in a hot coffee, the coffee will cool off based on the concept of heat transfer.
The coffee is at a higher temperature compared to the spoon, hence there is conduction of heat by the spoon from the coffee.
Heat is now transfered from the coffee to the spoon, the rate of heat transfer ( for this case coffee to spoon) is dependent on some properties but for this case, the thermal conductivity is of the most important.
A material of high thermal conductivity have a very fast rate of heat transfer and a material of low thermal conductivity have a slow rate of heat transfer.
Below is the value of thermal conductivity for copper, aluminum, iron and glass.
Copper (385 w/m.K)
Aluminum (205 W/m.K)
Iron (79.5 W/m.K)
Glass (0.8 W/m.K)
It can been seen that copper has the highest value for thermal conductivity which implies that it will conduct heat faster compared to others thus cooling the coffee faster.
D) Less than 20.
Explanation:
Equivalent resistance in a parallel combination is less than their individual value.
Answer:
u=78.4m/s
Explanation:
A ball is thrown vertically upward, which is the positive direction.A little later it returns to its point of release.The ball is in the air for a total time of 8.0 s.What is its initial velocity? Neglect air resistance
from newtons equation of motion
s=ut
v=u+at
v=0 because at maximum height reached by the ball the ball stops moving
0=u-9.8*8
u=78.4m/s
u=initial velocity
v=final velocity
a=acceleration due to gravity, 9.81m/s^2
t=time it takes in air
s= distance to get to the maximum before returning
