If the object is in equilibrium that means that the sum of the forces on it is zero and the net force is zero. If none of the forces changes then the object continues in constant uniform motion. That means constant speed in a straight line.
Answer:d
Explanation:
Alpha particles are heaviest among alpha, beta and gamma so they have least amount of Penetration compared to both.
Gamma Particles are lightest among three so they can Penetrate most .
The order of Penetration is given by
Alpha< Beta < Gamma
Answer:
(a) 
(b) 15 hours
Explanation:
half life, T = 12 hours
No = 19 g
(a) Let N be the amount remaining after time t.
Let λ be the decay constant.

The equation of radioactivity used here is given by


(b) N = 8 gram
Substitute the values in above equation

λ = 0.0577 per hour
So, 

Take natural log on both the sides
- 0.0577 t = - 0.865
t = 15 hours