11. Work and Energy – Class 9 Science | NCERT Chapter-wise Important Questions and Answers (CBSE)

Chapter 11: Work and Energy – Class 9 Science NCERT | Chapterwise Important Questions and Answers (CBSE)

Chapter 11: Work and Energy

Example 11.1:  A force of 5 N is acting on an object. The object is displaced through 2 m in the direction of the force (Fig. 11.2), then find the work done .

Solution: Here, F = 5 N and S = 2 m

  The work done (W) = Force (F) × Displacement (S)

= 5 × 2 J = 10 J

1. A force of 7 N acts on an object. The displacement is, say 8 m, in the direction of the force (Fig. 11.3). Let us take it that the force acts on the object through the displacement. What is the work done in this case?

 

        

Solution: Here, F = 7 N and S = 8 m

  The work done (W) = Force(F) × Displacement (S)

= 7 × 8 J = 56 J

Example 11.2 :  A porter lifts a luggage of 15 kg from the ground and puts it on his head 1.5 m above the ground. Calculate the work done by him on the luggage.

Solution: Here, Mass , m = 15 kg and displacement, s = 1.5 m.

Work done, W = F × s = mg × s

= 15 kg × 10 ms-2 × 1.5 m

= 225 kg m s-2 m

=225kg m²s-2

= 225 N m = 225 J

Work done is 225 J.

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Posted 4 months ago