Physics Help !!!!!!!

Also, because it's moving in circular motion, then we can say the force providing the centripetal acceleration is equivalent to $\frac{mv^{2}}{r}$

Hence:

$LSin\theta = \frac{mv^{2}}{r}$

I got $Lsin\theta = mg$

My right angled triangle looks like this:

I got $Lsin\theta = mg$

My right angled triangle looks like this:

By the way, you have the assigned the wrong angle to your right angled triangle which is why you're getting the horizontal component = mg.

You can tell this cannot be the case because there is no horizontal component of mg; weight always acts downwards so it is impossible for the horizontal component to equal a vertical component. You could be getting confused with inclined planes where the force parallel to the slop is equal to $mgsin\theta$

I was using Paint :P

So you do it by seeing what works rather than drawing a diagram? I can't think of a reason for the angle in my triangle to be anywhere else :/

I was using Paint :P

So you do it by seeing what works rather than drawing a diagram? I can't think of a reason for the angle in my triangle to be anywhere else :/

So you need to use both your intuition and the aid of a diagram. Here's why your angle is wrong:


The diagram on the right shows us when the plane is travelling parallel to the ground, so theta is equal to 0. Notice how the question states that the lift force always acts perpendicular to the wing. This is key because it tells us what even when the plane tilts over, this angle between the wing and lift force remains the same, at 90 degrees.

So now imagine the plane slowly rolling to one side (mine shows it rolling over to the left). You will find the the angle between the wing and horizontal increases (the angle theta). But you will also find the the angle between the vertical and L must also increase because remember, the angle between L and the wing must remain at 90 degrees, hence the angle between the vertical and L will increase the same as theta. You can see this with my diagram. Just think about it, imagine the wings rolling over and imagine the force L always remaining perpendicular to the wing.

Thanks so much! That was so useful! I assume if you made a triangle using that free body diagram you would correctly resolve the forces.

Much appreciated!

So you need to use both your intuition and the aid of a diagram. Here's why your angle is wrong:


The diagram on the right shows us when the plane is travelling parallel to the ground, so theta is equal to 0. Notice how the question states that the lift force always acts perpendicular to the wing. This is key because it tells us what even when the plane tilts over, this angle between the wing and lift force remains the same, at 90 degrees.

So now imagine the plane slowly rolling to one side (mine shows it rolling over to the left). You will find the the angle between the wing and horizontal increases (the angle theta). But you will also find the the angle between the vertical and L must also increase because remember, the angle between L and the wing must remain at 90 degrees, hence the angle between the vertical and L will increase the same as theta. You can see this with my diagram. Just think about it, imagine the wings rolling over and imagine the force L always remaining perpendicular to the wing.