Answer:
The speed of a wave would be 18 with a wavelength of 2 m and a frequency of 9 Hz.
Answer:
The apparent weight is the weight of the body minus the weight of the liquid displaced. The body will float only when both the weights are same. In this case, the given body of weight W is floating and hence the apparent weight is zero.
Answer : The temperature of the hot reservoir (in Kelvins) is 1128.18 K
Explanation :
Efficiency of carnot heat engine : It is the ratio of work done by the system to the system to the amount of heat transferred to the system at the higher temperature.
Formula used for efficiency of the heat engine.

where,
= efficiency = 0.780
= Temperature of hot reservoir = ?
= Temperature of cold reservoir = 
Now put all the given values in the above expression, we get:



Therefore, the temperature of the hot reservoir (in Kelvins) is 1128.18 K
Yes eventually because everyday we take in so much of those natural rescourses and eventually it is gonna go away because we used it all up