Answer:
Required charge
.

Explanation:
Given:
Diameter of the isolated plastic sphere = 25.0 cm
Magnitude of the Electric field = 1500 N/C
now
Electric field (E) is given as:

where,
k = coulomb's constant = 9 × 10⁹ N
q = required charge
r = distance of the point from the charge where electric field is being measured
The value of r at the just outside of the sphere = 
thus, according to the given data

or

or
Required charge
.
Now,
the number of electrons (n) required will be

or

or

Answer: 9/10
Explanation:
because it's really important and makes you energetic
Answer:
Value that the spring constant k = 12Mg / h
Explanation:
According to 2nd law of Newton:
upward force of the spring= F
The weight of the elevator W = mg
F = Mg = M(5g)
==> F =6Mg.
As the spring is compressed to its maximum distance ie s,the maximum upward acceleration comes just , Hence
F =ks = 6Mg
==> s = 6Mg/k
We have gravitational potential energy turning into elastic potential of the spring as the elevator starts at the top some distance h from the spring, and undergoes a total change in height equal to h + s, so:
Mg(h+s) = 1/2ks2
And plugging in our expression for s:
Mg(h+6Mg/k)= 1/2k(6Mg / k)2
gh + 6M2g2/k = 1/2k(36M2g2 /k2)
Mgh +6M2g2/k = 1/2k(36M2g2 /k2)
gh + 6Mg2/k = 18Mg2 / k
gh = 12Mg2 / k
h = 12Mg / k
k = 12Mg / h
Wave speed = frequency * wavelength
We need to rearrange this equation because we are finding the wavelength :
Wavelength = wave speed / frequency
To rearrange it, I just divided it by frequency so that wavelength was the subject.
Now, input these numbers into this equation :
Wavelength = wave speed / frequency
Wavelength = 25 / 5
Wavelength = 5m