There is a net force of 15N in The direction of Levi
(a) 
The gravitational potential energy of the two-sphere system is given by
(1)
where
G is the gravitational constant
is the mass of sphere A
is the mass of sphere B
r = 1.8 m is the distance between the two spheres
Substitutign data in the formula, we find

and the sign is negative since gravity is an attractive force.
(b) 
According to the law of conservation of energy, the kinetic energy gained by sphere B will be equal to the change in gravitational potential energy of the system:
(2)
where
is the initial potential energy
The final potential energy can be found by substituting
r = 1.80 m -0.60 m=1.20 m
inside the equation (1):
U=-\frac{(6.67\cdot 10^{-11})(94 kg)(100 kg)}{1.2 m}=-5.22\cdot 10^{-7} J
So now we can use eq.(2) to find the kinetic energy of sphere B:

Answer:
Option B
It converts light into electric current
Explanation:
A photometer is a device used to measure illuminance
Its principle of operation hinges on the conversion of light into electric current, using photoresistor or any other light sensitive device such as a photodiode. This is so that it can be read off easily by any other device.
A Photoresistor is a device that changes the flow of current through it when it is exposed to light rays. A photometer works by irradiating a photo resistor, which then converts the light rays incident on it to electric current.
The derivative of
h(t) = (-g/2)t² +v0·t + h0
is
h'(t) = -gt +v0
This is zero at the maximum height, so the time can be found as
0 = -gt +v0
gt = v0
t = v0/g