Answer:
Minimum coefficient of kinetic friction between the surface and the block is 
.
Explanation:
Given:
Mass of the block = M
Spring constant = k
Distance pulled = x
According to the question:
<em>We have to find the minimum co-efficient of kinetic friction between the surface and the block that will prevent the block from returning to its equilibrium with non-zero speed. </em>
So,
From the FBD we can say that:
⇒ Normal force, 
<em>...equation(i)</em>
⇒ Elastic potential energy, 
= 
<em> ...equation (ii)</em>
⇒ Frictional force, 
= 
<em> ...equation (iii)</em>
⇒ Plugging (i) in (iii).
⇒ 
Now,
⇒ As we know that the energy lost due to friction is equivalent to PE .
⇒ 
<em>...considering PE as</em> 
or 
.
Arranging the equation.
⇒ 
⇒ 
<em>...eliminating x from both sides.</em>
⇒ 
<em>...dividing both sides wit Mg.</em>
Minimum coefficient of kinetic friction between the surface and the block is .
The net force acting on the object perpendicular to the table is
∑ F[perp] = F[normal] - mg = 0
where mg is the weight of the object. Then
F[normal] = mg = (15 kg) (9.8 m/s²) = 147 N
The maximum magnitude of static friction is then
0.40 F[normal] = 58.8 N
which means the applied 40 N force is not enough to make the object start to move. So the object has zero acceleration and does not move.
Explanation:
One of the moments most valued by astronomers is twilight. As the Sun sets, the sky darkens and the first stars are seen. At first there are two or three, but as the minutes go by they become more and more visible; the first to appear will be the brightest stars of the night, the last, the dimmest. But their brightness is not the only thing that differentiates the stars. As the night progresses and the sky darkens, if we look closely, we will see stars of red, white and blue… Stars have colours, and learning about them takes us on a fascinating journey through their lives.
During these early spring weeks, it is easy to locate the constellation of Orion, along with Canis Major and Taurus, shortly after sunset. At first sight, the stars might appear to have the same colour, but if we seek out a dark sky and take a second closer look, we will notice different colours. Sirius (in Canis Major) is white, Rigel (Orion’s right foot) is blue, Aldebaran (in Taurus) is orange and Betelgeuse (Orion’s left shoulder) is red.
Answer:
#_photon = 7 10²¹ photons
Explanation:
Let's look for the power that affects the panel of area of 1.5 m2
I = P / A
P = I A
P = 1.37 10³ 1.5
P = 2,055 10³ W
P = E / t
If we use t = 1 s
E = P t
E = 2,055 10³ J
This is the power that the panel receives, let's look for the energy of a photon
E = h f
c = λ f
f = c /λ
E = h c /λ
Let's calculate
E₀ = 6.63 10⁻³⁴ 3 10⁸/680 10⁻⁹
E₀ = 2.925 10⁻¹⁹ J
In one second the total energy is the number of photons for the energy of each one
E = #_photon E₀
#_photon = E / E₀
#_photon = 2,055 10³ / 2,925 10⁻¹⁹
#_photon = 7 10²¹ photons
