What is the meaning of 'Force Acting Obliquely'?

 

Sometimes, movement of body is not in direction of force applied

F force is applied in different direction but body moves in a different direction

This is called force acting obliquely or force acting indirectly

In this case, there is an angle between direction of force applied and direction of movement of object.

Example

When a child pulls a toy car with a string

force applied is in different direction but car moves forward in different direction (making an angle)

Force acting obliquely.png

How to calculate work done in case of Force Acting Obliquely

In this case, we cannot use the formula

Work = Force × Distance


In this case, we cannot use Force because force is not in direction of movement of object

In this case, we cannot use the formula

So our formula becomes

Work = Force × Distance × cos θ

where θ is the angle between distance and force

 

Common Values of Cos θ

Some common values of cos θ for angles 0, 30, 45, 60, 90 are

DEGREE COS THETA VALUE
30 Degree √3/2
60 Degree 1/2
90 Degree 0
180 Degree -1
45 Degree 1/√2
0 Degree 1

Questions

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  1. Class 9
  2. Chapter 11 Class 9 - Work and Energy

Transcript

Question A child pulls a toy car through a distance of metres on a smooth, horizontal floor. The string held in child’s hand makes an angle of 60° with the horizontal surface. If the force applied by the child be 5N, Calculate the work done by the child in pulling the toy car. Force = F = 5 N Distance = s = 10 m Angle between force and distance = 𝜃 = 60° We know that, Work done = Force × Distance × cos 𝜃 = 5 × 10 × cos (60) = 50 × 1/2 ("cos 60 = " 1/2) = 25 J Work done is 25 J

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CA Maninder Singh
CA Maninder Singh is a Chartered Accountant for the past 9 years and a teacher from the past 16 years. He teaches Spoken English, Written English, Grammar and Vocabulary at Englishtan.