Electrical energy is the starting and final energy of a battery
To solve this problem it is necessary to apply the equations related to the Force of Friction and Energy.
By definition the friction force is defined as

Where,
Frictional Constant
N = Normal Force -> mg
At the same time we have the definition of the Energy, which can be
E = F*v
Where,
Force
v = Velocity.
Then replacing with our values we have that,

F = 0.5 *34
F = 17
The energy then would be,
E = f v
E = 17 * 0.30 = 5.1 W
Therefore the rate at which heat is generated is 5.1W
Your answer is B.
The relationship between medium temperature and speed of sound is a direct relationship: when one factor increases, the other increases as is shown in graph B. The British would choose the the time of day which would give the lowest speed of sound, because this would be easiest to break. Graph B shows that the lowest speed of sound would occur with the lowest air temperature - in the morning.