Tagged Questions
0
votes
1answer
49 views
Short-duration forces
In circular motion, it is said that the centripetal force acts only for a very very short period of time, hence is able to only change the direction but not magnitude of the velocity.
Similarly in a ...
-3
votes
0answers
23 views
Length Traveled from Complete Stop [closed]
A one-meter long rifle fires a bullet at a velocity of 800 m/s. What is the average acceleration experienced by the bullet when it is fired? (Hint: You need to find the time it takes the bullet to ...
-2
votes
1answer
32 views
Static friction force on a block in a tunnel
Linked to this Comparing Static Frictions
Suppose there is a cuboidal vertical tunnel , and a cubical block in it such that all surface of the block are in contact with the four walls of the ...
1
vote
2answers
141 views
Centripetal Force Acceleration
Suppose you want to perform a uniform circular motion . Then a body performing uniform circular motion horizontally needs an acceleration $= \frac{v^2}{r}$ at each point on the circular path with ...
-1
votes
0answers
39 views
Velocity versus time graph [closed]
A stone is thrown at an angle of $45^0$ above the horizontal x-axis in the +x-direction. If air resistance is ignored, which of the velocity versus time graphs shown above best represents $v_x$ ...
1
vote
3answers
67 views
Relation between the time, velocity and acceleration
This is question from I.E. Iredov's General Physics:
$1.22$ : The velocity of a particle moving in the positive direction of the $x-axis$ varies as $v = α \sqrt x$, where $α$ is a positive ...
13
votes
1answer
199 views
Modelling the movement and jumps of a chalk while drawing a dashed line on a blackboard
You probably know that if you try to draw a line using a piece of chalk on a blackboard , under some conditions (for example, $\alpha<\frac{\pi}{2}$ in the picture below) you will have a dashed ...
1
vote
2answers
128 views
How can I solve for time without knowing the vertical velocity?
A guy posted this problem on a forum:
There is a bird sitting on a pole of height h. you throw a rock at it and the moment the rock leaves your hand the bird starts flying horizontally away from ...
7
votes
1answer
255 views
Is acceleration an average?
Background
I'm new to physics and math. I stopped studying both of them in high-school, and I wish I hadn't. I'm pursuing study in both topics for personal interest. Today, I'm learning about ...
0
votes
3answers
100 views
Solve for Initial Velocity of a projectile given Angle, Gravity, and Initial and Final positions?
I've found equations http://www.physicsclassroom.com/Class/1DKin/U1L6a.cfm for solving everything (and rearranged to solve everything) to do with projectile motion EXCEPT this, even though it should ...
0
votes
1answer
84 views
Kinematics with non constant acceleration
A particle experiences an acceleration described by
$$
a=kx^{-2}
$$
where x is the displacement from the origin and k is an arbitrary constant.
To what value does the velocity v of the particle ...
15
votes
5answers
275 views
Does the mass point move?
There is a question regarding basic physical understanding. Assume you have a mass point (or just a ball if you like) that is constrained on a line. You know that at $t=0$ its position is $0$, i.e., ...
0
votes
5answers
173 views
Why is momentum conserved (or rather what makes an object carry on moving infinitely)?
I know this is an incredibly simple question, but I am trying to find a very simple explanation to this other than the simple logic that energy is conserved when two items impact and bounce off each ...
0
votes
1answer
46 views
Projectile's angle in midflight
For a missile travelling from (0,0) at angle $\theta$ (to the horizontal) and initial velocity $u$, the y (vertical) position at time t is given by
$s_{y} = u\sin (\theta) t - 0.5gt^{2}$
and the x ...
0
votes
1answer
70 views
Circular motion and centrifugal force
Assuming a race car drives around in a circle of radius r, center (0,0), linear velocity v, and ignoring centrifugal forces and friction I can calculate the position at any time, t.
Angular velocity
...
1
vote
0answers
74 views
What is the initial velocity of a projectile so that it passes through a target point in its trajectory? [closed]
Let's say I have a projectile being thrown by a player in my 2-D game. I want to work backwards and find the initial velocity to apply to the projectile such that it passes through a target point in ...
1
vote
1answer
71 views
Shooting a bullet at a system of blocks [closed]
So, I made this question up myself.... and I'm curious about the answer. It requires only secondary-school-level knowledge of physics:
You have a surface (ground) with a certain coefficient of ...
0
votes
2answers
143 views
Equation of motion for average acceleration
I am trying to solve the following:
A man of mass 83 kg jumps down to a concrete patio from a window ledge only 0.48 m above the ground. He neglects to bend his knees on landing, so that his ...
-3
votes
3answers
72 views
Speed of an object in air versus in vacuum
Okay, imagine that you are shooting a rocket down a tunnel that is 60 miles long and the rocket is travelling at 60mph, so the rocket should reach the end of the tunnel in a hour, right? Yep, in an ...
1
vote
0answers
53 views
I need help with the following Physics' questions [closed]
I need to know which formulas and the step-by-step answers for the following physics questions:
1. You throw a ball upward with an initial speed of 7.0 m/s, and it returns to your hand o.92 ...
3
votes
3answers
119 views
When can one write $a=v \cdot dv/dx$?
Referring to unidimensional motion, it is obvious that it doesn't always make sense to write the speed as a function of position. Seems to me that this is a necessary condition to derive formulas ...
2
votes
3answers
149 views
In projectile motion, what does it mean for the motion along the $x$ and $y$ axis to be independent?
In projectile motion, what does it mean for the motion along the $x$ and $y$ axis to be independent?
This question is referring to the concept of projectile motions.
1
vote
2answers
92 views
Why does gravity assist transfer twice the planet's velocity?
In orbital mechanics and aerospace engineering a gravitational slingshot (also known as gravity assist manoeuver or swing-by) is the use of the relative movement and gravity of a planet or other ...
1
vote
1answer
178 views
Monkey and tree - projectile motion
The famous scenario: A hunter is trying to shoot a Monkey hanging from a tree. However, this question doesn't mention the monkey jumping down from the tree or trying to escape. (The hunter uses a ...
1
vote
1answer
143 views
Projectile motion in two and three dimensions question?
So I bought this book in the library and physics fascinates me and I found this quote in the book " Galileo has proved that when any effects due to air resistance
are ignored, the ranges for ...
0
votes
2answers
108 views
Non-zero higher time derivatives of position?
My mom told me to use speed control, which would allow the car to remain at constant speed. I told her that its impossible for a car to maintain constant speed, as slight changes in friction on the ...
0
votes
2answers
167 views
Calculating vertical velocity component of a particle with mass, given the hit point of parabolic motion
Consider the following situation:
I have a particle with a given mass that at a given instant of time (let's say $t_{0}$) is placed at the system origin. The particle has a constant velocity ...
0
votes
0answers
78 views
Physics question motion in two dimensions? [closed]
A ball jumps from the plane and the ball has the acceleraion 500 m/s^2...the ball falls into the ground for 3 seconds..the speed of the plane is 500 m/s headed to east.Determine the position and the ...
0
votes
0answers
72 views
Downhill projectile question [closed]
I have to solve the following problem:
A hill is sloped downward at an angle $\theta$ with respect to the horizontal. A projectile of mass $m$ is fired with speed $v_0$ perpendicular to the hill. ...
0
votes
0answers
26 views
Intuitive understanding of the equation for kinetic energy [duplicate]
Possible Duplicate:
Why does kinetic energy increase quadratically, not linearly, with speed?
I know this is one of the easiest equations out there and I've used it for years but its still ...
14
votes
6answers
3k views
Is two cars colliding at 50mph the same as one car colliding into a wall at 100 mph?
I was watching a youtube video the other day where an economist said that he challenged his physics professor on this question back when he was in school. His professor said each scenario is the same, ...
0
votes
1answer
140 views
Two Different Sorts of Inertia: Inertial Mass and Moment of Inertia
There are two different sorts of inertia: inertial mass and moment of inertia.
I am currently reading about moment of inertia. Now, I know inertia is an important concept; with it, we can determine ...
7
votes
5answers
440 views
How can kinetic energy be proportional to the square of velocity, when velocity is relative?
Let's start with kinetic energy (from los Wikipedias)
The kinetic energy of an object is the energy which it possesses due to its motion. It is defined as the work needed to accelerate a body of a ...
0
votes
1answer
185 views
Solving inclined plane using diff. frame
I was trying to solve frictionless inclined plane problem using a diff. frame as shown in the figure, and can't figure out that acceleration along the plane = g.sin(Θ), but I think it should be = ...
0
votes
0answers
499 views
Finding the period and frequency for simple harmonic motion [closed]
A 1 lb weight is suspended from a spring. Let y give the deflection (in inches) of the weight from its static deflection position, where “up” is the positive direction for y. If the static ...
2
votes
1answer
113 views
Parabolic Motion
I was wondering if I was right about this simple problem:
A projectile is shot at an angle of 37.0° with the horizontal. The velocity of the projectile at its peak height is 16 m/s.
Then I was told ...
2
votes
1answer
112 views
helium balloon tied to a car [closed]
A helium balloon is tied to the seat of a car. The doors and windows of the car is closed. If the car now starts moving, in which direction will the balloon move- front or back?
1
vote
2answers
304 views
Calculating force required to stop bungee jumper
Given that:
bungee jumper weighs 700N
jumps off from a height of 36m
needs to stop safely at 32m (4m above ground)
unstretched length of bungee cord is 25m
Whats the force required to stop the ...
0
votes
2answers
972 views
Acceleration/tension of object. 1 on horizontal surface one hanging
A 5.00-kg object placed on a frictionless, horizontal
table is connected to a cable that passes over a pulley and
then is fastened to a hanging 9.00-kg object, as in Figure. Find
the ...
1
vote
1answer
543 views
Newton 2nd Law: Does vertical force (mass) affect the horizontal acceleration?
I learnt before that if 2 forces are perpendicular to each other, they should not affect each other. However in a recent experiment setup (asked in another question):
I believe the theoratical ...
2
votes
1answer
466 views
Determine acceleration from experiment (Newton 2nd Law)
I have done a physics experiment (setup below). And was asked to determine the experimental and theoretical acceleration.
The data I've got
Ok, am I right to say
Experimental acceleration ...
0
votes
2answers
288 views
Center of gravity of vehicle and vehicle performance
I am interested to know how does CG of vehicle plays role in the Fuel economy and the vehicle performance. Does CG of vehicle has anything to do while accelerating of your vehicle. I am a student, ...
0
votes
1answer
126 views
Proving $t=(1+\sqrt{1+2hg/v^2 } ) (v/g)$ for a thrown ball
If we throw a ball from the hight point $h$ from the earth, with initial velocity $v’$, how to prove that the time it takes the ball to reach the earth is given by:
...
0
votes
0answers
74 views
Jumping on a landing pad [closed]
I'm trying to make a character jump on a landing pad who stays above him. Here is the formula I've used (everything is pretty much self-explainable, maybe except character_MaxForce that is the total ...
2
votes
1answer
197 views
What is the longest distance that can be jumped after swinging from a rope?
In the movie Mission Impossible 3, the main character Ethan Hunt tries to enter a building in Shanghai by swing through the sky, as shown below:
The jump consists of 2 sections, the red part, which ...
0
votes
0answers
104 views
How do I solve this Kinematics question? [closed]
In 1987, Art Boileau won the Los Angeles Marathon, 26 miles and 285 yards, in 2h, 13 minutes and 9 seconds. At the 21-mile mark, Boileau had a 2.50 min lead on the second place winner, who later ...
0
votes
0answers
202 views
Projectile Motion
I know the angle at which a projectile is launched, how far it needs to go, and also the maximum height. How can I find the initial velocity needed (disregarding air resistance)?
Currently, I am ...
-1
votes
1answer
89 views
Simulating a car in an intersection
I'm somewhat confused. I want to simulate in real-time an intersection where cars have to turn left, right or go straight. What I have are 2 way points: One at the beginning of the intersection on ...
4
votes
5answers
2k views
Why there is a 1/2 in kinetic energy formula? [duplicate]
Possible Duplicate:
Why is there a $\frac 1 2$ in $\frac 1 2 mv^2$?
Hèllo, I have a question about kinetic energy formula.
As you know, in kinetic energy formula, we have:
...
0
votes
2answers
724 views
Preventing a block from sliding on a frictionless inclined plane
I want to demonstrate what force $F$ you would have to exert on an inclined plane of angle $t$, mass $M$ to prevent a block on top of it with mass $m$ from sliding up or down the ramp. I worked out ...
