A certain element is a clear, stable gas at room temperature. An atom of this element has 7 protons, 7 electrons, and a mass number of 15. How many neutrons are in this atom?

Number of neutrons = 8

Given

7 protons, 7 electrons, and a mass number of 15.

Required

Number of neutrons

Solution

Within the atom there are subparticles, namely protons, neutrons and electrons

Protons and neutrons are present in the atomic nucleus, while electrons surround the atomic nucleus in the atomic shell

Atomic number = number of protons = number of electrons

Mass number= number of protons + number of neutrons

15 = 7 + number of neutrons

number of neutrons = 8

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(newtons first law)

conservation of momentum law states :

momentum before collision = momentum after collision

momentum p (kg-m/s)= mass * velocity

say moving car=1 000 kg, velocity = 10 m/s then p = 1 000*10= 10 000 kg-m/s

say still car = 2 000 kg, velocity = 0 m/s then p = 2 000* 0 = 0 kg-m/s

total momentum prior to collision = 10 000 + 0 = 10 000 kg-m/s

momentum after collision = 10 000 kg-m/s

mass now = 1 000 kg+2 000 kg = 3 000 kg

10 000 = 3 000 kg* velocity m/s

10 000/3 000 = velocity

3.33 m/s = velocity after collision

an impulse is a force applied over time , momentum is exclusive of external forces and a perfect collision is implied