1. why did the discovery of nuclear reactions cause the separate laws of conservation of matter and conservation of energy to be combined into the law of conservation of mass-energy? (points : 3)
- matter is not conserved in nuclear reactions because some of the matter is converted to energy.

- nuclear reactions happen too quickly for changes in energy to be measured.

- energy is conserved in nuclear reactions but not in chemical reactions.

- only particles that move at the speed of light can overcome the laws of conservation.

A: Matter is not conserved in nuclear reaction because some of the matter  is converted to energy.

Explanation:

A nuclear reaction is of two types : fission and fusion

Fission nuclear reaction: A nuclear reaction in which two heavy nuclei split into lighter nuclei and release a large amount of energy . The mass of heavy nuclei is slightly greater than the total mass of reactant . The difference between mass of product and reactant is change into energy.

Fusion nuclear reaction: A nuclear reaction in which tow or more lighter nuclei combined together and form heavy nuclei of mass is slightly less than the combined mass of reactants nuclei.A large amount of energy is released in this nuclear reaction. The difference between the mass of products and reactants is convert into energy.

Therefore, It does not follow the law  conservation of mass but, when energy released and mass of products combine then the addition sholud be equal to mass of reactants.Hence, the discovery of nuclear reactions cause the separate laws of conservation of matter and conservation of energy to be combine into  the laws of conservation of mass-energy.

Therefore, option A is true.

Answer A: Matter is not conserved in nuclear reaction because some of the matter  is converted to energy.

answer: 2×10^-2kg

explanation: density= mass per volume

vol=mass/density

converting to s.i units we have;

3÷1000kg = 0.003

1.5÷100m = 0.15

0.003/0.15 = 0.02kg