Christian Lawson-Perfect

Christian Lawson-Perfect on Find the foci of an ellipse 9 years, 5 months ago

Gave some feedback: Doesn't work

Christian Lawson-Perfect commented on Force acting on an object at an angle with friction 9 years, 5 months ago

You've got "tan" in plain text instead of LaTeX in a few places.

The sentences "Therefore $P$ must exceed $x\, \mathrm{N}$" could do with a couple more words: "Therefore $P$ must exceed $x\, \mathrm{N}$ in order for the mass to start moving", or "The mass will move if $P$ exceeds $x \, \mathrm{N}$".

Christian Lawson-Perfect commented on Maximum frictional force acting on a mass 9 years, 5 months ago

A sentence with two whiches in it is hard to parse. You could rewrite the statement like so:

A mass of $x \, \mathrm{kg}$ rests on a rough horizontal plane. Find the maximum frictional force which can act on the mass, in the following situations.

In the advice, I'd be happy saying the reaction force cancels out the force due to gravity, without going through $F=ma$. Up to you though.

You've got a few separate scenarios, and using information parts to set them up. Instead, I'd collect related parts into a single gapfill, so you can use the prompt to set up each scenario. That is, you can merge each of (c,d,e), (f,g,h) and (i,j,k).

Christian Lawson-Perfect commented on Resolve forces into components 9 years, 5 months ago

You could add steps to each of the parts: find the component of $F_1$ in the $x$-direction, then find the component of $F_2$ in the $x$-direction, and finally add them together to get the resultant force in the $x$-direction.

Christian Lawson-Perfect commented on Resolve forces into components 9 years, 5 months ago

I'd rename the variables shown to the student as follows:

• Forces $F_1$ and $F_2$, and angles $\theta_1$ and $\theta_2$.
• Let $F = F_1 + F_2$.

Then you can say "find the component of $F$ in the $x$-direction".

Or, if you don't want to give away that the student should add the forces, say "Two forces, $F_1$ and $F_2$ are acting on a particle at the origin. Let $F$ be the resultant force on the particle".

Christian Lawson-Perfect commented on Resolve force into $x$ and $y$ components 9 years, 5 months ago

Same comments as the other question: use \sin and \cos, and give units.