A mobile phone is 35% efficient. Over half an hour 11 kJ of energy is transferred to the phone.
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Answer:
The question is incomplete,below is the complete question
"Calculate the number of atoms contained in a cylinder (1μm radius and 1μm deep)of (a) magnesium (b) lead."
Answer:
a. 1.35*10^{11} atoms
b. 1.03*10^{11} atoms
Explanation:
First, we determine the volume of the magnesium in the cylinder container
using the volume of a cylinder
a. Next we determine the mass of the magnesium ,
using the density=mass/volume
since density of a magnesium
Finally to calculate the number of atoms,
we determine the number of moles
mole=mass/molarmass
Hence the number of atoms is
number of atoms=mole*Avogadro's constant
b. for he lead, we determine the mass of the lead ,
using the density=mass/volume
since density of a magnesium
Finally to calculate the number of atoms,
we determine the number of moles
mole=mass/molarmass
Hence the number of atoms is
number of atoms=mole*Avogadro's constant
(a) 1.01 cm
First of all, we need to find the spring constant of the spring.
The force initially applied to the spring is equal to the weight of the block hanging on it:
where m = 4.32 kg is the mass of the block and g = 9.8 m/s^2 is the acceleration of gravity.
When this force is applied, the spring stretches by
We can find the spring constant by using Hooke's law:
where k is the spring constant. Solving for k,
Later, the first object is removed and another object of mass
m' = 1.50 kg
is hung on the spring. The weight of this object is
So, if we use Hooke's law again, we can find the new stretching of the spring:
(b) 1.16 J
The work that must be done on the spring is equal to the elastic potential energy that would be stored in the spring, therefore:
where we have
k = 1448.6 N/m is the spring constant
x = 4.00 cm = 0.04 m is the new stretching
Solving the equation, we find the work that must be done by the external force: