If you are driving 72 km/h along a straight road and you look to the side for 4.0 s, how far do you travel during this inattenti
1 answer:
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A. Lithium
The equation for the photoelectric effect is:
where
is the energy of the incident light, with h being the Planck constant, c being the speed of light, and
being the wavelength
is the work function of the metal (the minimum energy needed to extract one photoelectron from the surface of the metal)
K is the maximum kinetic energy of the photoelectron
In this problem, we have
, so the energy of the incident light is
Converting in electronvolts,
Since the electrons are emitted from the surface with a maximum kinetic energy of
K = 4.0 eV
The work function of this metal is
So, the metal is Lithium.
B. cesium, potassium, sodium
The wavelength of green light is
So its energy is
Converting in electronvolts,
So, all the metals that have work function smaller than this value will be able to emit photoelectrons, so:
Cesium
Potassium
Sodium
C. 4.9 eV
In this case, we have
- Copper work function:
- Maximum kinetic energy of the emitted electrons: K = 2.7 eV
So, the energy of the incident light is
Then the copper is replaced with sodium, which has work function of
So, if the same light shine on sodium, then the maximum kinetic energy of the emitted electrons will be
We must place the pivot to keep the meter stick in balance at 90 cm (10 cm from the weight) from the free end.
Answer: Option B
<u>Explanation:</u>
In initial stage, the meter stick’s mass and mass hanged in meter stick at one end are same. Refer figure 1, the mater stick’s weight acts at the stick’s mid-point.
If in case, the meter stick is to be at balanced form, then the acting torques sum would be zero. So,
Taking out ‘mg’ as common and we get
Hence, the stick should be pivoted at a distance of,
So, the stick should be pivoted at a distance of 75 cm at the free end
Now, replace mass with another mass. i.e., four times the initial mass (as given)
If in case, the meter stick is to be at balanced form, then the acting torques sum would be zero. So,
Taking out ‘mg’ as common and we get
Hence, the stick should be pivoted at a distance of,
So, the stick should be pivoted at a distance of 10 cm from the free end.
Therefore, the option B is correct 90 cm (10 cm from the weight).
Answer:
Final speed of the crate is 15 m/s
Explanation:
As we know that constant force F = 80 N is applied on the object for t = 12 s
Now we can use definition of force to find the speed after t = 12 s
so here we know that object is at rest initially so we have
Now for next 6 s the force decreases to ZERO linearly
so we can write the force equation as
now again by same equation we have
put t = 6 s