# Civil Engineering - Applied Mechanics - Discussion

Discussion Forum : Applied Mechanics - Section 1 (Q.No. 47)
47.
Two forces act an angle of 120°. If the greater force is 50 kg and their resultant is perpendicular to the smaller force, the smaller force is
20 kg
25 kg
30 kg
35 kg
40 kg.
Explanation:
No answer description is available. Let's discuss.
Discussion:
8 comments Page 1 of 1.

Amsal said:   3 years ago
50 * COS(180 - 120) = 25.
(1)

Mayur said:   5 years ago
I think it is solved by simple trignometry.

Gagan said:   5 years ago
120/50=2.4.
Then 180-120 = 60 then 60/2.4 = 25.

Hanan said:   5 years ago
Kg is not the unit for force.

Sanchit Mathur said:   5 years ago
Lami's Theorem says;

P/sinα = Q/sinβ = R/sinγ

In the above question, P=50, Q is the force perpendicular to smaller force and R is the smaller force;
α=90 , β=120, γ=360-(90+120).

This gives R as 25kg.

Subha Annadurai said:   6 years ago
How to use lami's theorem? Explain please.

Kishor said:   6 years ago
Here, we can also use Lami's theorem.

Abhay said:   8 years ago
Resultant force makes an angle α with the force P(in this case smaller force).

tanα = Qsinθ/(P+Qcosθ) α = 90, θ = 120, Q = 50, P =?

tanα = sinα/cosα = 1/0.

1/0 = Qsin(120)/(P+Qcos(120)) means P+Qcos(120) = 0.

Therefore P = -Qcos(120) = -50cos(120) = -50*(-1/2) = 25kg.