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Question 18N.3.SL.TZ0.6b.ii

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Date November 2018 Marks available [Maximum mark: 2] Reference code 18N.3.SL.TZ0.6b.ii
Level SL Paper 3 Time zone TZ0
Command term Outline Question number b.ii Adapted from N/A
b.ii.
[Maximum mark: 2]
18N.3.SL.TZ0.6b.ii

A uniform rod of weight 36.0 N and length 5.00 m rests horizontally. The rod is pivoted at its left-hand end and is supported at a distance of 4.00 m from the frictionless pivot.

The support is suddenly removed and the rod begins to rotate clockwise about the pivot point. The moment of inertia of the rod about the pivot point is 30.6 kg m2.

(b.ii)

After time t the rod makes an angle θ with the horizontal. Outline why the equation θ = 1 2 α t 2  cannot be used to find the time it takes θ to become  π 2 (that is for the rod to become vertical for the first time).

[2]

Markscheme

the equation can be applied only when the angular acceleration is constant ✔

any reasonable argument that explains torque is not constant, giving non constant acceleration ✔

 

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