What is the change in internal energy if 70 j of heat is added to a system and the system does 30 j of work on the surroundings?

a. 40 j
b. 100 j
c. -40 j
d. -100 j

I think the answer is A. 40 J

Explanation:

Hope it helps

when insulating materials rub against each other, they may become electrically charged . electrons , which are negatively charged, may be 'rubbed off' one material and on to the other. the material that gains electrons becomes negatively charged. the material that loses electrons is left with a positive charge.

1 - wave length

2 - amplitude

3 - crest

4 - trough

explanation:

duh.