Easy question has me confused (Inclined plane)

In summary, the 10lb block A slides down a plane with a constant velocity when θ=30°. The acceleration of the block when θ=45° is 9.62 ft/s^2.
  • #1
jamesweston0
26
0
It seems to be an easy question but for some reason I can't figure it out.

Homework Statement



2vbsw2x.jpg


If the 10 lb block A slides down the plane with a constant velocity when θ = 30°, determine the acceleration of the block when θ = 45°.

Homework Equations



F = ma

The Attempt at a Solution



I actually am very puzzled by this question. I know that acceleration = 0 at 30° but I don't know how to make use of it. I tried setting the parallel force at 45° to equal ma, then solve for a, but that didn't do it either. Any insight? Thanks.
 
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  • #2
first resolve the forces around the block
 
  • #3
FNormal = 10cosθ
Fparallel = 10sinθ

Just sub in 30 and 45 for θ.

What else is there to use?
 
  • #4
where is gravity in your equation remeber its the force of the block acting down the slope not the mass. Just want to check do you assume that the plane is smooth?
 
  • #5
Well the 10sinθ is the force of gravity down the ramp. Also, yes I'm assuming the plane is smooth. It doesn't say anything to lead me to believe there's friction.
 
  • #6
it should be the force of the block acting down the ramp so 10gsin45=ma

but since the mass is the same
should get gsin45=a
 
  • #7
Hmm I though 10lb is referring to a force not a mass in this case.

Regardless, gsin45 = a is not working out.

32.2sin45 = 22.77 ft/s^2

The real answer is 9.62 ft/s^2.
 
  • #8
hmmm not sure then. ill have another look
we both must be missing something obvious :/
 
  • #9
Yeah lol this is really confusing for me too. It doesn't seem to be very hard but something is obviously not clicking.
 
  • #10
Any new ideas?
 
  • #11
The only reason I think they would give you the 30 degree condition is that you need to account for friction.

try using the 30 degree criteria to get the coefficient of friction.
 
  • #12
You got it rock.freak667!

Kind of a weird question since it didn't say anything about friction. It's not in the friction chapter either. It's a few chapters later. I guess they expect us to use ideas from previous chapters even without making mention of them.

Thanks!
 
  • #13
jamesweston0 said:
It seems to be an easy question but for some reason I can't figure it out.

Homework Statement



2vbsw2x.jpg


If the 10 lb block A slides down the plane with a constant velocity when θ = 30°, determine the acceleration of the block when θ = 45°.

Homework Equations



F = ma

The Attempt at a Solution



I actually am very puzzled by this question. I know that acceleration = 0 at 30° but I don't know how to make use of it. I tried setting the parallel force at 45° to equal ma, then solve for a, but that didn't do it either. Any insight? Thanks.
You would use the 30 degrees to solve for the kinetic friction and then use the value for kinetic friction to solve for the acceleration. I believe its supposed to be a trick question since nowhere is friction mentioned. Cannot be solved without first finding the friction which happens to be 0.5774. Find the Normal force, and with the friction you should come out with the answer. Hope this helps.
 

Related to Easy question has me confused (Inclined plane)

What is an inclined plane?

An inclined plane is a simple machine that is a flat surface set at an angle, allowing objects to be moved from a lower point to a higher point with less force than it would take to lift the object directly.

How does an inclined plane work?

An inclined plane works by reducing the amount of force needed to move an object to a higher point. By increasing the distance over which the force is applied, the amount of force needed is decreased. This is known as mechanical advantage.

What are some examples of inclined planes?

Some common examples of inclined planes include ramps, slides, and staircases. Other examples include roadways that go up hills, wheelchair ramps, and even the wedge-shaped end of a doorstop.

What is the formula for calculating the mechanical advantage of an inclined plane?

The formula for calculating the mechanical advantage of an inclined plane is MA = length of slope/height of slope. This means that for every unit of height the object moves, it will travel a certain number of units along the slope.

What are some real-world applications of inclined planes?

Inclined planes have a wide range of applications in everyday life. They are used in construction for building ramps and staircases, in transportation for roads and highways, and in manufacturing for loading and unloading materials. Additionally, inclined planes are used in medical equipment, such as wheelchair ramps, and in sports equipment, such as ski slopes and skate ramps.

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