Very powerful, breaking within ten seconds (7)
I believe the answer is:
intense
'very powerful' is the definition.
'intense' can be an answer for 'powerful' (intense can mean powerful or profound). I am not sure about the 'very' bit.
'breaking within ten seconds' is the wordplay.
'breaking' indicates putting letters inside.
'within' becomes 'in'.
'ten' becomes 'tene' (I can't justify this - if you can you should give a lot more credence to this answer).
'seconds' becomes 's'.
'in'+'tene'='intene'
'intene' going around 's' is 'INTENSE'.
Can you help me to learn more?
(Other definitions for intense that I've seen before include "Strongly-felt" , "Showing strong feelings or opinions" , "In an extreme degree" , "Strong in quality or degree - perhaps a feeling" , "Strong in degree or emotion" .)