Answer:
option (c) is correct
Explanation:
Half life of a substance is the time in which the element becomes half of is initial value.
half life, T = 8 days
Amount remaining, N = 10 % of original value
Let the original value is No.
N = 10% of No
N = 0.1 No
Let the time taken is t and the decay constant is λ.
The relation between the decay constant and the half life is given by

Us the equation of radioactivity



Taking natural log on both the sides, we get
0.08664 t = 2.303
t = 26.6 days
Answer:
0.488 m
Explanation:
If θ be the angle ladder makes with the plane
cos θ = 1.2 / 5
Tan θ = 4.04
Let the height a person of weight 600 N can climb be h from the ground .
Distance from the base point where ladder touches the floor = h / tanθ
= h / 4.04
Total reaction force = total downward force
R = 200 + 600
800 N
Frictional force = μ R
= .2 x 800
= 160 N
Taking moment of force about the point on the ladder where it touches the floor and balancing them
200 x 1.2 x .5 + 600 x h / tanθ = μ R x 1.2 / tanθ ( reaction at the top point of ladder where it touches the wall is R₁ and
R₁ =μ R )
= 200 x 1.2 x .5 + 600 x h / tanθ = 160 x 1.2 / tanθ
120 - 600 h / 4.04 = 47.52
120 - 47.52 = 600 h / 4.04
72.48= 148.51 h
h = 0.488 m
=
The gravitational pull is weaker.
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