# What is Mechancis: Definition and 131 Discussions

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1. ### I Why does the main muscle use the most energy in body movements?

This may seem like an obvious and foolish question intuitively, but I am curious about something. Let's assume we are performing a biceps curl exercise. To properly analyze human movement, a much more complex process is needed, but I will simplify it as much as possible. As the name of the...
2. ### B Why in two block systems do both blocks tend to have the same velocity?

So giving two examples where this happens Example 1 Consider a hemispherical bowl and a block placed inside it if the bowl is given velocity v𝑣 and given that there is no friction, the block will gain kinetic energy and then will rise to a maximum height h both the bowl and block will have same...
3. ### I Friction Clamp Conundrum

Hi guys, I am trying to design a brake/locking mechanism to hold up a weight, here is some background; I have a weight 18kg, 170mm away from the pivot point on an arm. A brake compresses the arm at the pivot point. This consist of a M10 bolt compressing a surface area of 1500mm^2 on each side of...
4. ### How to input and output work in a system at the same time?

Basically, I thought of a weight as a energy storage. But realised you have to output that energy from the same part that inputs the energy. Now I have done some research and found two ways of storing and discharging mechanical work at the same time. First is the Huygens mechanism(maintaining...
5. ### A Is the Approach for Verifying Lagrangian Acceptable?

Hi Guys Please refer to the attached document for my derivation. The image presents the system in plan view, I know one my think that it is unstable structure based on a single pinned connection however this is a simplification of a complex structure sitting on a slew bearing. Gravity does...
6. ### Calculating Force and Acceleration in a Two Block System with Varying Friction

in the A we need to find the force and acceleration of the system when we pull the lower block and the upper mass starts to move in B we need to find the force and acceleration of the system when we pull the upper block and the upper mass starts to move the friction before the lower mass and...
7. ### Confused on whether this counts as an external torque

For part (d), there is the formula a = v^2/r I can use. Note that Mg = mv^2/r, we have two unknowns, v and r. I can solve this if conservation of angular momentum is true, i.e. mvr = constant. I am not convinced I can use this however, because is increasing M torque? My idea is that it is an...

9. ### What is the physics behind performing a wheelie on a motorcycle?

I need to understand the mechanics involved in performing a wheelie. That includes analyzing the free-body diagram. And considering all the factors involved in performing this manoeuvre in motorbilkes.
10. ### Understanding Work-Energy Theorem: Solving an Exercise with Different Solutions

My solution is different from the official solution and I don't understand what I did wrong. Here is my solution: The magnitude of the initial velocity is ##|v_0| = 12.0~\rm{m/s}##, so the vertical component of the initial velocity is ##v_{0-y} = (12.0 \sin{25^{\circ}})~\rm{m/s}##. Then I use...
11. ### Mechanics for High School Students: Building a Robotic Arm

TL;DR Summary: Mechanical engineering,robotics,mechnics,dynamics Hi guys , I'm new to mechnics and I want to learn it for building robotic arm , but I find mechanics book topics somewhat difficult for me , what I need to learn to get started as I'm a highschool student with basic level math.
12. ### Engineering Is My Free Body Diagram for a Frame Accurate?

can you check if I sketched it correctly? And please if you know any good resources refrence it.
13. ### Variable mass, uniform body, force -- pulling a massive rope

So i got some equations but i think i am missing something, my main doubt is what is the relation between dx / dt and v(o) [ here] . Workings in attachment
14. ### Did I Miscalculate the Speed for a Leaking Cart Under Acceleration?

My approach is to use the definition of the Force with ##\displaystyle F = \frac{dp}{dt} = \dot{m} v + m \dot{v}##. Since ##m(t)## decreases linearly, I should be able to set ##m(t) = M - \Phi t##, thus ##F = - \Phi v + (M - \Phi t) \dot{v}##, which gives ##\displaystyle v = -\frac{ F - (M -...
15. ### Conservation of momentum and mechanical energy on an inclined plane

So i am tried to conserve momentum and use conservation of mechanical energy but won't there be psuedo force acting on the block if i am solving from non inertial frame ?. If i ignore the pseudo force and simply use C.O.M.E and include the K.E of the wedge and solve normally i do get the...
16. ### I Understanding Holonomic Constraints: Common Questions and Answers

I've got a couple of questions concerning holonomic constraint equations: 1- Suppose I've got k holonomic constraint equations for n particles, how can I be sure those are all the ones there are and I didn't miss any? I mean, in a given situation, I can be pretty sure that I've got all, but is...
17. ### I Can I always consider velocities and coordinates to be independent?

It's a topic that's been giving be a headache for some time. I'm not sure if/why/whether I can always consider velocities and (independent) coordinates to be independent, whether in case of cartesian coordinates and velocities or generalized coordinates and velocities.
18. ### I Terminal Velocity proportional to the Drag Force 𝑚𝛾𝑣² in free fall

Can anyone help me? I know that's wrong, but i don't know where. Thanks for your attention so far.
19. ### From circular orbit to elliptical orbit

Problem: a particle of mass m is in a circular orbit around a planet at a distance R from the center. The planet mass is M and it's radius is R_0. What is the tangential impulse that will cause the particle to brush against the back of the planet? Describe the orbit. The attempt at solution...
20. ### To find the angle between the ground and rods in limiting friction

Could I please ask for help with the following: Here's my diagram: The forces at the hinge (green) are internal forces. For the whole system resolving vertically gives: R1 + R2 = 4W and horizontally gives: F1 = F2 For the rod of weight 3W only, taking moments about B gives: F1 * L *...
21. ### Vertical spring connected between two bodies with a rope above them

Question: A string spring is connected between two bodys with a rope above them. M1 = 25Kg M2 = 50KG Distance between them is 100m. I answered a bit and got to the point where the distance between the two masses are 110m ( the mass below got 10m lower and is on balance, I mean, acceleration = 0...
22. ### B Creep and its effects on a material

What I do not get is why should a stress much lower than yield point cause deformation in a material? If temperature is high intermolecular attraction is reduced and thus even low stress can deform things. But if it is low Then a force lower than yield point should be less than intermolecular...
23. ### A Change of a vector in a rotating coordinate system

Goldstein 3 ed, pg 171, under" rate of change of a vector " : The author derives the relationship between the change of a vector in a stationary and rotating coordinate system. In the process he uses this assumption :>It is no loss of generality to take the space and body axes as...
24. ### I Adhesive Collision: Coding for Sticky Objects

I am trying to code collision of two objects. When they collide, instead of rebound or motion of them according to their velocity, i want them to stick together and move in direction of resultant normal velocity. It is not plastic collision. I want a force that stops the rebound. how can i...
25. ### Torque calculations: Rotating vertical shaft

I apologize in advance for any errors in my concepts or assumptions. Feel free to correct me wherever I am wrong. Thanks in advance for the help. There is a vertical shaft which will be operated at around 600 rpm (N) which can be achieved in 2 seconds (or even 4 just an assumption). The shaft...
26. ### To find the resultant of forces on a lamina

Could I please ask for help with the following question: A lamina is in the shape of an equilateral triangle ABC, and D, E, F are the midpoints of BC, CA, AB respectively. Forces of magnitude 4N, 8N, 4N, 3N, 3N act along AB, BC, CA, BE, CF respectively, the direction of each force being...
27. ### Rolling 3 objects on an inclined plane

Hello there, I have a question regarding this problem. I have no problem with part A. However, in part B, my solution manual states that the hollow cylinder will reach the bottom last. Why is it? I mean shouldn't the solid cylinder and the hollow one reach the bottom at the same time? you know...
28. ### How to calculate the magnitudes of three forces around a hexagon

Can anyone please help me with the following? Three forces which act along the sides AB, BC and CD of a regular hexagon ABCDEF of side 2a, have a resultant which acts along DF. When a couple of 4Pa in the sense CBA is added in the plane of the hexagon, the resultant acts along CA. Find the...
29. ### Conservation of Energy Problem (Power)

Hello there, I was trying to solve this problem. I have no problem with part A and C. But in part B, my guidebook arrived with different answer. Can anybody point out what my mistake is? I am using the same method as the elevator motor problem which states : "A 650-kg elevator starts from rest...
30. ### Estimate the initial velocity of the cars after the collision

What came to my mind for this question is: Consider one of the cars. The velocity and mass of this car are V and M respectively. And the velocity and mass of the piece attached to the car are m, v respectively. Before the collision, the velocity of this piece relative to this car is zero. So its...
31. ### The motion of a charged particle in a magnetic field

qvB=mv^2/R R=mv/qB= p/qB ! As you can see, the difference between this relation and the relation in question is in 'c'. Maybe my way is wrong. Maybe I should get help from relativity because the speed of light is involved here. Please help. Thankful
32. ### Conservation of energy problem: Two masses, a pulley and an incline

If M moves ##x## along the plane, her height variation in ##x \cos(\alpha)##, and, but I don't know how to find the variation of the height of ##m##
33. ### Calculating the time to cross a river

Could I please ask for help on the last part of this question: So, part b, I get the right time but not the right distance. Book answers are: distance = 1/6 and time = a/V. Here's my (faulty?) reasoning (LaTeX isn't working for me): The boat is steered due east and so would have a velocity...
34. ### To find the time to nearest appoach of a dinghy and a buoy

Can anyone please help me see if my reasoning is correct regarding the following question? I'll just solve for the case where the dinghy tracks so as to just 'touch' the exclusion zone on the 'high' side So, in the diagram below: The dinghy tracks along the red path, inclined at x degrees...
35. ### Influence of initial shift on undamped frictionless forced oscillations

I have general equation for undamped forced oscillations (no friction) which is: I just wonder about,what type of motion should occur when initial conditions are both 0 (i.e v0=0 and x0=0). My intuitive expectation is that as there is no 'natural' oscillations at beginning,vibration has to be...
36. ### To find the time for which a vessel is within range of these guns

Could I please ask for help with the following question (the second part): A cruiser sailing due north at 24 km/h sights a destroyer 48 km due east sailiing at 56 km/h on a course (360-a) degress where cos(a)=11/14. Show that the destroyer's course realtive to the cruiser is on a bearing of...
37. ### To find the time taken for one vessel to reach another

Could I please ask for help regarding my answer to the following question? I've done the first part and get the answer of 500 seconds. I anticipated no problem with the second part, it is the same problem with different inputs, but I have disagreed with the provided answer of 1754 seconds. I...
38. ### Finding motion where the acceleration depends on position and time

I have computed that the acceleration in my problem is a(t) = -gj - k/m(|r(t)| - L_0) * r(t)/|r(t)| Where a(t) is the acceleration vector, g is the gravitational acceleration, j is the unit vector in y-direction, k is the spring constant, m is the mass, r(t) is the position vector, |r(t)| is...
39. ### Mechanics: Slope Friction Problem

So far, I have this: For Part ii) I know that: mgh = xmgsin(theta), but I don't know how to go further

41. ### A cart with two cylindrical wheels connected by a rod

Firstly I only consider one of the wheels. This wheel consists of a big wheel (black) with mass M and radius R and inside it a circular region with a negative mass (-m) and radius R/2. (I assume they have same mass density but with opposite signs. I do this because I don't know where the center...
42. ### Velocity of an object on an inclined plane

I used work energy theorem between initial top point and point x along the incline(downwards) i got the expression of v then diffrentiated it to get a maxima but it gives me a wrong ans which is 10/6 but the actual ans is 10/3 please tell me what i did wrong
43. ### Calculation of minimum angular velocity of a mass on a spinning plate

Problem Statement: How to calculate minumum angular velocity of a mass on a spinning plate Relevant Equations: f=mrw^2 Hi, here's the question: a) A rough horizontal plate rotates with a constant angular velocity of w about a fixed vertical axis. A particle of mass m lies on the plate at a...
44. ### I How Is Particle Distribution in a Solid Angle Derived in Mechanics?

I'm reading Mechanics by Landau and Lifshitz, chapter IV, and trying to understand how in a (closed) center of mass system, with randomly distributed and oriented particles that disintegrate, "the fraction of particles entering a solid angle element ##do_{0}## is proportional to ##do_{0}##, i.e...
45. ### Solving Torsion Spring Problem with 100 lb Force

I am struggling through a problem in one of my designs and would appreciate some help. Please refer to the image attached. Problem Description: S = Torsion spring F = fixed point T = tire A tire is attached to a torsion spring through an arm as shown in the image. The torsion spring has one...
46. ### Prove: angular momentum is preserved

3. Find the hamilton equations 4. using 3. prove the the angular momentum in the z axis ##L_z=m(x\dot y-xy\dot)## is preserved. I got in ##3##: How can I prove 4?
47. ### What is the angle between the velocity of and the normal to the racket?

My approach: Let us take two orthogonal axes: x, parallel to the racket's plane and y, perpendicular to it. For the ball to not spin, the components of initial velocities of the racket and the ball along x-axis must be same. Also, as the line of collision is along the normal to the racket's...
48. ### Why Does My Relative Density Calculation Not Yield a Numerical Value?

So I am a bit stuck on this question as my result using the above equations dose not give an numerical value which I assume from the question is needed. So here my method for solving My first thought was that if on the planet the person can throw a rock 10 time further then that it implies in...
49. ### 2 objects connected by a spring - Minimum Force required to move the objects

On object 2: There are only 2 horizontal forces - Friction and Tension (of the spring). T = km2g On Object 1: There are 3 horizontal forces and the minimum value for F is when: F - km1g - km2g = 0 F = kg(m1 + m2) However, Solution is: F = kg(m1 + 0.5 m2) Any opinion?
50. ### Using first principles, how to get the equation of motion?

<< Mentor Note -- thread moved from the technical forums, so no Template is shown >> Show, from the first principles, that the equation of motion of a mass (m) on a spring, subjected to a linear resistance force R, a restoring force S, and a driving force G(t) is given by d2x/dt2+ 2K(dx/dt) +...