Force Diagrams [Hinge Questions]

This question comes fresh from teaching Mechanics 1; for assessing whether students can draw force diagrams involving motion.

hinge1_1

a) Student has selected the diagram where R is not perpendicular to the surface on which the object sits.
b) Student has selected the diagram with an additional force (friction) onto the diagram, where the question states a smooth slope
c) Student has selected the diagram with an additional force in the direction of motion; showing they believe that resultant forces should be drawn on the diagram.
d) Student forgot that acceleration should be represented on the diagram
e) Correct diagram
f) Student has selected a diagram that shows the correct forces, but has forgotten that the weight of the object should include the acceleration due to gravity. (note this could also show the student believes g to be a unit)

More mechanics themed questions to follow.

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3 Responses to Force Diagrams [Hinge Questions]

  1. jnewman85 says:

    I think I’m gonna steal this for my class since we’re on the topic, thanks!

    Do you ask students to explain why the other diagrams are wrong? Also, do leave open the possibility that more than one is right?

    Lastly, I guess you’ve covered in your class how “smooth” means “frictionless”. I’m a Physics teacher (though I’m not a very good one) and I wouldn’t have known that smooth means frictionless. In fact, I’d say that in the real world smooth means something more like “less friction” rather than “frictionless”. If there’s one thing I’d change for my class, it’d be changing the word “smooth” to “frictionless” in the problem. Or perhaps something like “negligible friction for modeling purposes”.

    Thanks for the question!

    • nik_d_maths says:

      Hi! I usually like to have 2 right answers among the 6, but it was difficult to do that in this situation.

      When using questions like this I sometimes group students with the same misconception and then get them to explain so we can fix it.

      Smooth is used because it’s the language our students are expected to understand – I agree that frictionless is waaay better – feel free to change!

      Thanks 🙂

  2. Pingback: 7 Days of Maths https://spectatormaths.wordpress.com #5 | Solve My Maths

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