6. D
7. D
8. B
let me know if you need clarification
Answer:
320 N/m
Explanation:
From Hooke's law, we deduce that
F=kx where F is applied force, k is spring constant and x is extension or compression of spring
Making k the subject of formula then

Conversion
1m equals to 100cm
Xm equals 25 cm
25/100=0.25 m
Substituting 80 N for F and 0.25m for x then

Therefore, the spring constant is equal to 320 N/m
Answer:
Heat Transfer
Explanation:
This is called heat transfer. Heat transfer is the process in which energy flows from a matter that is higher in heat to a matter that is cooler, until the two matters reach the same temperature.