Missing part in the text of the problem:
"<span>Water is exposed to infrared radiation of wavelength 3.0×10^−6 m"</span>
First we can calculate the amount of energy needed to raise the temperature of the water, which is given by

where
m=1.8 g is the mass of the water

is the specific heat capacity of the water

is the increase in temperature.
Substituting the data, we find

We know that each photon carries an energy of

where h is the Planck constant and f the frequency of the photon. Using the wavelength, we can find the photon frequency:

So, the energy of a single photon of this frequency is

and the number of photons needed is the total energy needed divided by the energy of a single photon:
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Answer:
(5g/cm³)*(10cm³) = 50g
Explanation:
This is just a conversion formula. Easy to find using dimensional analysis.
(5g/cm³)*(10cm³) = 50g
Answer:
4
Explanation:
G = Gravitational constant = 6.67 × 10⁻¹¹ m³/kgs²
= Mass of Earth
= Mass of Moon
r = Distance between Earth and Moon
Old gravitational force

New gravitational force

Dividing the equations

The ratio is 
The new force would be 4 times the old force
Answer:
1 / f = 1 / i + 1 / o thin lens equation
1 / i = 1 / f - 1 / o = (o - f) / (o * f)
i = o * f / (o - f)
i = 54.2 * 12.7 / (54.2 - 12.7) = 16.6 cm image distance
Image is real and inverted and 16.6 / 54.2 * 6 = 1.94 cm tall