-1
votes
0answers
24 views

Kinematics of point moving on a circle [closed]

Let $A$ be a fixed point on a circle. Let a point $P$ move along the circle in such a manner that the acceleration vector always points to $A$. Show that the acceleration is proportional to ...
-1
votes
1answer
17 views

What should be used, $v=r \omega$ or radial and transverse components? What would be the next step? [duplicate]

An aircraft A is flying in a vertical plane containing two tracking stations P and Q which are 15km apart. At a cetain instant θ (measured anticlockqise from horizontal line PQ to the line PA) is 60° ...
1
vote
1answer
62 views

i can't detect what wrong have i done in a kinematics problem [closed]

a question was given to us in assignment which was as follows A person moves 20 metres towards north then 30 metres towards east and then moves 30 x 1.414 metres towards south west. The whole ...
0
votes
1answer
64 views

$\theta '' = \frac{a}{R}$? [closed]

Assume that this is a general circular motion where $\theta$ is a function of time. I've derived some equations below and found that the angular velocity in the end is zero. Which step of my ...
1
vote
2answers
106 views

Kinematics question - Newton's Law of Motion [closed]

Question: Find the mass M of the hanging block in the following figure which will prevent the smaller block from slipping over the triangular block. All the surfaces are frictionless and the strings ...
0
votes
1answer
29 views

Kinematics - moving body [duplicate]

If I have an inclined plane, which has acceleration $\alpha$, will a block placed on the inclined plane slip back with the same acceleration? (considering that the surface is frictionless)
-2
votes
2answers
38 views

How to know the Direction of the Acceleration Vector?

If the exercise doesn't give you the direction, how to know the correct one? Sometimes I assume its to the right and it was actually to the left, and I get everything wrong. Example here: How can I ...
1
vote
2answers
50 views

Weird Kinematics Homework [closed]

Here's another "hard" homework question I was given on how printers work. (I find it more confusing than it is hard.) I'm supposed to find the horizontal velocity of a charged droplet as it leaves ...
0
votes
0answers
28 views

How to calculate the equation of projectile motion for curved ramps? [duplicate]

Consider the following cases (these are sections): I can find the equation of motion for Case a however I don't know how to deal with Case d. Normally I would need the angle α otherwise I can't ...
1
vote
0answers
34 views

Finding the time of convergence for this system of particles [closed]

Point A moves uniformly with velocity $v$ so that the vector $\vec{v}$ is continually "aimed" at point B which in turn moves rectilinearly and uniformly with velocity $u < v$. At the initial ...
1
vote
2answers
136 views

Proof of centripetal acceleration formula ($a_c = \frac{v^2}{r}$) for non-uniform circular motion

The formula for centripetal (radial) acceleration is well known, and there exist many proofs for it: $$||a_c|| = \frac{||v||^2}{r}$$ However, all the proofs I've seen rely on the fact that it is ...
1
vote
2answers
63 views

What's The Minimum distance?

My Friend gave me a question today. The question was.:: We have a point A. At a distance of $x_0$ from the point. There is a particle$(P_1)$. Also, a particle is present at the point A $(P_2)$.The ...
1
vote
1answer
39 views

Kinematics simple question [closed]

Question: In order to protect himself from the rain, a person is standing holding an umbrella at right angle to the horizontal surface. The rain is falling at 10m/s when the velocity of the wind is ...
1
vote
2answers
46 views

Why is the constant velocity model used in a projectile motion derivation?

I was re-studying university physics last week, I'm now in the chapter about kinematics in 2 dimensions and specifically the one treating projectile motion. In page 86 of his book (Serway - Physics ...
0
votes
2answers
42 views

Finding out the velocity [closed]

Displacement of an object is related to time $x=at+bt^2-ct^3$ where a, b and c are constant motion.Then the velocity of an object when it's acceleration is zero is given by ...
0
votes
2answers
90 views

Kinematics - projectile motion on inclined plane [closed]

Well I've tried everything to solve this problem, spent well over an hour, and have gotten no results. A particle is thrown over a triangle from one end of a horizontal base it grazes the top vertex ...
0
votes
3answers
36 views

Kinematics - Concept of average velocity

Average velocity, as I have heard, cannot be found simply by finding the average of two numbers. I have a question on average velocity, but am simply unable to proceed: A particle moving in a ...
0
votes
1answer
25 views

Kinematics - ball bouncing off vertical walls [closed]

So here's my best attempt to state the question: A ball is thrown from a 100 meter tall tower, which has a vertical wall in front of it. The initial velocity of the ball is 10m/s and the distance ...
2
votes
1answer
51 views

Kinematic, motion in 2D [closed]

If the kinetic energy at maximum height is 2/5 the kinetic energy at half the maximum height, find the angle of projection. In other words: K.E. at H(max) = 0.4*K.E. at 0.5*H(max) I got 60 degrees, ...
-4
votes
3answers
33 views

Velocity and acceleration with displacement [closed]

Find the velocity and the acceleration for a moving object with displacement $= te^{-t}$. The $e$ is the exponential function.
1
vote
3answers
45 views

average speed and velocity [closed]

A distance on a straight line from point $a$ to $b$ is $2 km$. A student walks from this line with a speed of 4km/h and another student walks with a speed of 6km/hour. what is the average velocity and ...
1
vote
1answer
51 views

Understanding why a problem was solved a certain way

I have this question in one-dimensional kinematics and the way the book solves it has left me confused. Here's the question: ...
1
vote
2answers
43 views

Why is initial position negative? [closed]

A student on ground throws a ball straight up, the ball leaves students hand with speed of 15m/s when hand is 2.0mm above ground How long is the ball in the air before it hits the ground? I was ...
0
votes
2answers
33 views

Projectile motion - ball hit 180m/s at 45 degrees, what is the hang time? [closed]

Assuming no air resistance etc, how long is the ball in the air for? This is actually part of a longer question concerning the ball trajectory on different planets but I think there must be an easier ...
1
vote
1answer
41 views

Travel time for accelerating object [closed]

I have an object which starts at velocity = 0. Accelerates to a known max speed and continues thereon at constant velocity (max speed). My problem: How long does it take to reach a known ...
1
vote
3answers
228 views

Why is using Newton's First Law failing me?

A factory worker pushes a 29.7kg crate a distance of 5.0m along a level floor at constant velocity by pushing downward at an angle of 32$^\circ$ below the horizontal. The coefficient of kinetic ...
2
votes
1answer
45 views

How to get time from equation of linear uniformly accelerated motion?

I have had a problem solving this equation for time (from Linear Uniformly Accelerated Motion (LUAM)): $$ s= v_0t + \tfrac{1}{2}at^2 $$ I'll appreciate if someone could provide me some step-by-step ...
-2
votes
1answer
57 views

Kinematics - angle of projection given relation between speed at highest point and half of that [closed]

For a projectile launched from a point on horizontal ground, the speed when it is at the greatest height is $\sqrt{\frac{2}{5}}$ times the speed when it is at half of its greatest height. Determine ...
1
vote
2answers
106 views

Help with a solid sphere sliding and then rolling

Initially at time $t=0$, a solid sphere slides with velocity $v$ along a horizontal surface. The coefficient of friction is u. Find the required time for the sphere to stop sliding (the sphere will ...
-3
votes
1answer
63 views

Throwing an object in the air [closed]

Studying formulas about velocity and acceleration I came up with a question: if I throw an object in the air with a velocity $v_0$ (suppose i throw it vertically) in how much time its final velocity ...
2
votes
3answers
64 views

How to calculate the velocity of this body? [closed]

Graph of a train (the body) is provided which starts from rest. What is the velocity after the train has 10 metres displacement? Thats the only things provided for the question, please help me ...
0
votes
2answers
150 views

Is there a mistake in this example in my mechanics textbook?

This is a worked example in my mechanics book: But I think this worked example is wrong. In the 6th line. shouldn't $X=4R$ as the expression for distance above the surface is $(X-R)$ and when the ...
0
votes
2answers
97 views

Why does a perpendicular force not change speed?

I have been taught that a perpendicular force acting on an object will only change the direction of its velocity, not its magnitude. The explanation that was provided to me is that because there no ...
1
vote
2answers
52 views

Kinetic energy of a mass rotating about two axes

I'm working on a question where I have to find an equation for the kinetic energy of a mass being rotated by a fold-able arm. The equation for $m_1$ is obvious, however, the equation I derived for ...
1
vote
1answer
78 views

A ball is thrown up, and a second ball is dropped- what is the maximum initial velocity of the first ball so that

This question only exists in one dimension, the y axis. A ball is thrown upwards with an initial velocity $V_o$ from a roof with height $h$. One second later, a second ball is dropped from the same ...
1
vote
0answers
42 views

Uniform Circular Motion with Banked Road and Car [closed]

In Uniform Circular Motion, if a car is rounding a curve at a certain speed, and the angle of the road allows the car to drive around at that speed, that speed is called the "design speed." If the ...
0
votes
2answers
52 views

When solving kinematics questions, how to find time in air?

I was trying to help a friend with this question: A ball is shot horizontally off a cliff. What would happen to the horizontal distance it travels if the acceleration due to gravity were doubled ...
2
votes
0answers
93 views

Kinematics and Motion [closed]

If a body loses half of its velocity on penetrating 3cm in a wooden block, then how much will it penetrate more before coming to rest? How does answer come out to be 1cm?
-1
votes
1answer
46 views

Unknown Mass Spring Problem [closed]

A student conducts an experiment to measure the motion of two unknown masses (A and B) along a smooth table. A constant force of 1 N was applied by means of a string connected by a falling weight. A ...
8
votes
3answers
729 views

Number of planks required to stop the bullet [closed]

A bullet looses (1/n)th of its velocity passing through one plank. The number of such planks that are required to stop the bullet can be? Logically, to me the answer seems to be infinity, as always a ...
1
vote
0answers
49 views

How Long does it take for a roller coaster cart to reach point $x_1$? [closed]

Assume that we have a particle with weight m and initial speed v0, that follows a roller coaster path y(x). Assuming no energy loss to friction or air resistance, the total energy in the system is ...
0
votes
1answer
33 views

Compute the minimal distance between two points in movement

There are two points, $A$ and $B$ that move according to these laws: $$ \vec{x_a}= 20 -10 t $$ $$ \vec{x_b}= -15 +15 t $$ $A$ moves along the x axis, $B$ along the y axis. I have to compute the ...
0
votes
3answers
63 views

How can I compute the angular velocity of a triangle formed by three particles knowing their instantaneous positions and velocities? [closed]

I have a set of trajectories of three particles and their instantaneous velocities. I would like to compute the 3 components of the angular velocity pseudovector of the fictive triangle formed by ...
0
votes
1answer
46 views

Two equations for $y$ in projectile motions

I have two equations on my equation sheet: $$y=v_o t \sin \theta - \frac{1}{2} g t^2.$$ And then another: $$y_{\max} = \frac{v_o^2 \sin 2 \theta }{2g}.$$ I understand that the first one is an ...
0
votes
3answers
69 views

Why don't the kinematic equations agree with calculating velocity one second at a time?

A car is moving at a velocity of $10 \, \text{m}/\text{s}$. After point $A$ no acceleration is provided. By simple measurement, the acceleration is found to be $-1 \, \text{m}/\text{s}^2$. Using ...
0
votes
1answer
57 views

Is there any significance to the negative sign on this speed?

A girl is riding a bicycle along a straight road at constant speed, and passes a friend standing at a bus stop (event #$1$). At a time of $60$ s later the friend catches a bus (event #$2$) If the ...
0
votes
1answer
67 views

Is it possible to work out the shortest time in which a body can travel a certain distance if all that is provided is the max a, max -a, v1, v2 and s?

Is it possible to calculate the shortest time it takes a body to travel a certain distance if the only information provided is its maximum acceleration, its maximum retardation and the distance it ...
1
vote
2answers
218 views

Position dependent speed, how to compute position

I can't solve a problem: $ A= 0.5 (ms)^{-1}$, $ x_0 = 0.5 m $, $v(t)= A \cdot x^2 $, I have to compute the position at $t=3$ ($x_0$ is the initial position). So my guess is that I should be able ...
0
votes
1answer
66 views

Ball thrown in a moving train [duplicate]

A ball is thrown upward in a train moving with a constant velocity. Where will it land? My intuition tells me that the ball will fall at my back. But my book says that it will return back to the ...
0
votes
1answer
39 views

A pearl that moves in a smooth vertical hoop

I wanted to ask about the situation of a pearl that moves in a smooth vertical hoop in circular motion as described in the following sketch. According to a simulation found in the internet , a ...