Question

exercise Level-I
1.
An object of mass m is tied to a string of length I and a variable horizontal force is
applied on it which is initially is zero and gradually increases until the string makes an
angle e with the vertical. Workdone by the force F is​

Answer 1

Explanation:

: An object of mass m is tied to a string of length L and a variable horizontal force is applied on it which starts at zero and gradually increases until the string makes an angle θ with the vertical. Work done by the force F is:

(A) mgL(1-sinθ )

(B) mgL

(C) mgL(1-cosθ )

(D )mgL(1+cosθ )

Sol: Work done by the external force = Δ E of the system (object)

= ΔPE (since ΔKE=0 )

= mgh = mg (L – L cosθ )

= mgL (1 – cosθ )