Alokananda's Trick Block

Classical Mechanics Level 3

Alokananda keeps a block of mass $m$ on an incline inclined at angle $\theta$ . She finds that the block remains static.

What is the force exerted by the plane on the block?

Inspired by Alokananda Sarkar .

Image Credit : http://www.methodquarterly.com

mg

mg \cos \theta

mg \sin \theta

mg (\sin \theta + \cos \theta)

1 solution

Agnishom Chattopadhyay
Aug 18, 2016

The block is kept at rest by opposing the component perpendicular to the plane with its normal reaction and along the plane via friction. So, the total force must be the weight.

What made this simple problem look interesting was that most people only take only the normal reaction into consideration.

Aaa ._. I got it wrong :( I neglected friction but didnt realise that the block cannot be static without friction.

Ashish Menon - 4 years, 10 months ago

I made the same mistake when she asked me this problem

Agnishom Chattopadhyay - 4 years, 10 months ago

Nice question; I had to give it a second thought before answering. It might be more precise to start the last sentence as "What is the magnitude of the force exerted ....", since force is a vector and in this case has one component parallel and one perpendicular to the inclined plane.

Brian Charlesworth - 4 years, 9 months ago

Thanks, I have updated the wording.

Agnishom Chattopadhyay - 4 years, 9 months ago

Absolutely right, but I forgot to consider friction...good and interesting

Javier Martínez Dominguez - 4 years, 9 months ago

Alokananda's Trick Block

Inspired by Alokananda Sarkar .

Image Credit : http://www.methodquarterly.com

1 solution

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