Work is (force applied) x (distance through which the force moves).
Since the suitcase doesn't move up or down during the 15 minutes,
no work is done ... zero, zip, nada ... according to the real Physics
definition of 'work'.
The heat required to convert the unknown substance X from one phase to another is 1600 J times the specific heat of that substance.
Explanation:
The heat energy required to convert a substance or to heat up or increase the temperature of a substance can be obtained from the specific heat formula.
As per this formula, the heat energy applied should be equal to the product of mass of the substance with temperature gradient and also with specific heat of the substance. Basically, the heat provided to increase or convert a substance should be more than the specific heat of the substance.

Since, here the mass of the substance X is given as m = 20g and the temperature change is given from -10°C to 70°C.
Then ΔT = (70-(-10))=70+10=80°C.
As the substance is unknown, the specific heat of that substance can also not be determined. Hence keep it as C.

Q = 1600C J
Thus, the heat required to convert the unknown substance X from one phase to another is 1600 J times the specific heat of that substance.
I think it’s “light energy to chemical energy” let me know if i’m wrong
Since anjul is looking at samples on the counter, it's reasonable to assume that the environment is room temperature. The only metal liquid at room temperature is mercury
Answer:
1.2825 * 10^3 kg/m³
Explanation:
Given that :
Mass of aluminum ball (m1) = 4kg
Apparent mass of ball (m2) = 2.10 kg
Density of aluminum (d1) = 2.7 * 10^3 kg/m³
Density of liquid (d2) =?
Using the relation :
d1 / d2 = m1 / (m2 - m1)
(2.7 * 10^3) / d2 = 4 / (4 - 2.10)
2700 / d2 = 4 / 1.9
4 * d2 = 2700 * 1.9
4 * d2 = 5130
d2 = 5130 / 4
d2 = 1282.5 kg/m³
Hence, density of liquid = 1.2825 * 10^3