Answer:
Matter is radioactive and decays over time.
Explanation:
Becquerel and the Curies discovered the radioactivity.
The Curies died because they did a lot of experiments using Radio and other elements.
The other alternatives are concepts that are known for a long time.
Answer:
-1.09m/sec^2
Explanation:
Acceleration= (Vf-Vi)/Time
=12-54.8
= -42.8
= -42.8/39
=-1.09
-ve sign is due to recoil of train
as it suddenly hits brakes.
