A) Pure substances, Chemical changes
The correct option is
a fire
In fact, a fire is a conversion of chemical energy (contained in the molecules of the initial substances) into thermal energy (the heat released by the fire itself), therefore this is an example of energy changing from one form to another. All the other objects, instead, do not represent any form of energy conversion.
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Answer:
20m/s
Explanation:
Given parameters:
Distance of throw = 50m
Time = 3s
Unknown:
Average speed = ?
Solution:
Average speed is distance divided by time;
Average speed =
Insert the parameters and solve;
Average speed =
= 16.66667m/s = 20m/s
Answer:
The speed is
.
(a) is correct option.
Explanation:
Given that,
Potential difference 
Speed 
If it were accelerated instead
Potential difference 
We need to calculate the speed
Using formula of initial work done on proton

We know that,


Put the value into the formula

....(I)
If it were accelerated instead through a potential difference of
, then it would gain a speed will be given as :
Using an above formula,

Put the value of 



Hence, The speed is
.