All Questions
57 questions
-4
votes
3
answers
92
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How do you prove the formula for momentum? [closed]
I am just an absolute beginner to physics. I've seen a proof of the formula for momentum using Newton's second law of motion, but to prove Newton's second law of motion you have to use the formula for ...
0
votes
2
answers
55
views
Is the way of determining my angle of vector wrong or am I using the wrong formula for calculating magnitude of resultant? [closed]
i) Two balls A and B are simultaneously projected from top of building at 10m/s upward and 20m/s downward. Find distance between them after 3s? (Answer: 90m)
There are two magnitude of resultant ...
- 111
1
vote
1
answer
60
views
Conceptual difficulty with with component accelerations in polar coordinates
In kinematics why is the acceleration along the radius not the time derivative of the velocity along that radius?
1
vote
1
answer
71
views
Relation between fixed constraints and time derivative of the Lagrangian
I have had some trouble interpreting and proving the following statement from Fasano, Marmi's "Analytical Mechanics" (page 139):
"... ${\partial L}/{\partial t} \neq 0$ (1) only if the ...
- 402
-1
votes
1
answer
455
views
How to find the direction of acceleration if an object is changing its direction of velocity but not magnitude then how we can find the direction
I am new at this topic so please do mind if my question doest make sense to you.I am trying to find out that what will be the direction of acceleration if object changes Direction of velocity but not ...
0
votes
1
answer
87
views
Find the equation for the angle $\theta$ in which the particle leaves the semicircle. No Friction [closed]
I think I missed something in this mechanics problem.
We're given a polished (no friction) and homogeneous hemicircle which has mass $M$ and a particle of mass $m$ laying on the top of it.
There is ...
- 177
0
votes
2
answers
94
views
Normal reaction on a mass travelling along a curve
I've come across a set of problems in classical mechanics, where I am supposed to find the value of the normal reaction that acts on a mass, as it travels along a curve $y=f(x)$.
For example, suppose ...
- 1,853
-1
votes
2
answers
67
views
Q: How to find the height of lake given time [closed]
I'm struggling with a Kinematics homework question:
On a beautiful day you decide to go fishing with your younger brother Ben. Ben has not been fishing before so he doesn't know how to properly cast ...
0
votes
3
answers
238
views
Equation of motion of a classic inverted pendulum in free fall
I was thinking in this interesting problem:
Suppose we have this inverted pendulum:
But without this control force $F$ and the system would by loose from a height $h_0$, with initial velocity $0$ ...
0
votes
1
answer
187
views
How can the $x$-components of the frictional force and the normal force be the same for a static block on an incline? [closed]
I recently was assigned this problem as part of my homework:
"A block sits on a plane that is inclined at an angle $\theta$. Assume that the friction force is large enough to keep the block at ...
2
votes
4
answers
583
views
Why is a ball thrown in the air symmetrical in the time it falls
I’m having trouble with high school physics question.
The question is finding the time in the air of a ball that is thrown into the air with some initial velocity (negligible air resistance) and ...
- 21
-2
votes
1
answer
116
views
Regarding Uniform Acceleration [closed]
Please give some basic intuition or hint to solve this question. I'm getting stuck.
The star of a distant solar system explodes as a supernova. At the moment of the explosion, a
resting exploration ...
- 1
0
votes
2
answers
58
views
Inclined planes and motion [closed]
A particle of mass $2\;kg$ is fired up a smooth slope of length $4 \;m$, with initial speed $10\;m/s$, inclined at an angle $30^\circ$ degrees above horizontal. What is the speed of the particle at ...
- 63
1
vote
1
answer
86
views
Exact distance travelled by an object due to gravity only
I am aware of the fact that for two point masses in space, the time that it will take for them to collide is, T=$\pi \sqrt{\frac{r_i^3}{8GM}}$, where M is the sum of the 2 bodies' masses, $r_i$ is the ...
- 13
0
votes
2
answers
92
views
Elasticity of spring and conservation of energy [closed]
I have a problem of one of my students mechanics homework that I am unsure on and could do with resolving by tomorrow is possible! A spring of natural length $0.5m$ is attached to the ceiling and a ...
- 101
1
vote
4
answers
358
views
How to find motion equations using energy and angular momentum? [closed]
I'd really appreciate some help with an exercise.
The exercise presents a system of two bodies, $m$ and $M$. Both are connected with a weightless rope; the former is rotating (with a given initial ...
- 11
0
votes
1
answer
46
views
Distance of slowing object [closed]
I have object with a given mass $m$, which is moving with the velocity $v$ and there is force $\bf F$ pushing against movement of the object.
How far will object travel until it stops and how long ...
- 3
1
vote
5
answers
7k
views
Optimum launch angle for a projectile launched from a height above the ground [closed]
If a projectile is launched from a height greater than zero and landed to a height equal to zero, is the optimum launch angle that gives the greatest horizontal range still $45$ degrees or not?
I know ...
user282164
1
vote
1
answer
87
views
Finding the angle required to hit a stationary target [closed]
Ignoring air resistace, I have that the height of our canon is $8.2$m and the height of the target is $6.34$m. And that our initial veocity $v_0=18$m/s. I have to determine a way to find the angle ...
- 145
1
vote
1
answer
37
views
Determine the velocity by a projectile motion [closed]
A snowball rolls from the roof of a large barn that has a downward slope of 20 °. The roof end is 15.0 m above the ground and the snowball has a speed of 6.00 m / s when abandoned from the roof. At ...
- 13
2
votes
1
answer
128
views
Does mass matter at all for kinematics vertical questions w/o friction?
This is the specific question w/o information on mass given, I think here is not enough info.
A block and a sphere are each released from rest at the top of an incline from the same height. The ...
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-1
votes
1
answer
40
views
Vertical motion [closed]
Ball $A$ is thrown vertically upward from the top of a $30$ m high building with an initial velocity of $5$ m/s. At the same instant, another ball $B$ is thrown upward from the ground with an initial ...
0
votes
3
answers
678
views
Kinetic Energy and Braking Distance [duplicate]
A car traveling at 50km/h will move 44 extra meters from the moment its brakes are applied fully. If the same car travels 100 km/h on the same road, how far will it move from the instant its brakes ...
- 21
1
vote
2
answers
1k
views
Relative velocities in Circular Motion
Recently I saw the following interesting problem
Ann is sitting on the edge of a carousel that has a radius of 6 m and is rotating steadily. Bob is standing still on the ground at a point that is ...
- 199
0
votes
1
answer
771
views
Distance from ground to start suicide burn with initial height [closed]
In the figure below, the rocket is dropped with no initial velocity at a height of $h$. $d_f$ (free fall distance) is the distance in which the rocket is in free fall. $v_b$ is the velocity due to ...
- 103
0
votes
1
answer
1k
views
Finding tangential and normal velocity from a curve [closed]
How do you find tangential and normal velocity from a curve?
I know how to find dy/dx, but I have no idea how to obtain ut and un and dv/dt.
3
votes
2
answers
127
views
How to decelerate from velocity $v$ to stop time $t$ over distance $d$? [closed]
I'd be grateful for some help with this problem I am trying to solve.
Let's say that I have an object travelling at a velocity $v$. I want that object to come to a halt in time $t$ AND travel exactly ...
- 31
0
votes
2
answers
244
views
Why is the direction of net force on an object and the direction of acceleration of that object different in this problem?
A $ 2.0 kg $ box of cucumber extract is being pulled across a frictionless table by a rope at an angle $ \theta=60° $ (from positive direction of $ x $ axis, we have taken horizontal surface of table ...
0
votes
2
answers
15k
views
The human body can survive an acceleration trauma incident (sudden stop) if the magnitude of the acceleration is less than [closed]
The human body can survive an acceleration trauma incident (sudden stop) if the magnitude of the acceleration is less than 250 m/s². If you are in an auto- mobile accident with an initial speed of 105 ...
1
vote
2
answers
414
views
Inconsistent Results with Momentum and Kinetic Energy
A speed skater with a mass of $m_1$ kg is moving at $v_{1i}$ m/s. He prepares to push the next speed skater of mass $m_2$ kg moving at $v_{2i}$ m/s. After the push, the velocity of the first skater ...
- 121
1
vote
4
answers
2k
views
Intuition - why does the period depend on the amplitude in a pendulum?
I'm looking for an intuition on the relationship between time period and amplitude (for a large pertubation) of pendulums. Why does the period depend on the amplitude? I know the math of the problem. ...
- 53
-3
votes
1
answer
274
views
Projectile motion question : time at which velocity v becomes perpendicular to initial velocity u? [closed]
A projectile is thrown up with the initial speed u, making an angle theta (theta > 45 deg) with the horizontal. What is the time, just after which, it will be moving perpendicular to its initial ...
- 53
-1
votes
2
answers
45
views
Kinematic Approach
I was recently looking at a physics problem and it kind of confused me:
A 1 kg ball is shot out of a 5m long cannon directly upwards. A constant force of 15 N is used to accelerate the ball out of ...
0
votes
2
answers
1k
views
How to show angle between velocity and acceleration vector is constant in polar co-ordinates? [closed]
In polar co-ordinates we have
$\vec{r} = r\hat{r}$ and
$\vec{v} = \dot{r}\hat{r} + r\dot{\theta}\hat{\theta}$ and
$\vec{a} = (\ddot{r}-r\dot{\theta}^2)\hat{r} + 2\dot{r}\dot{\theta}\hat{\theta}$
...
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-2
votes
1
answer
250
views
Deriving an expression for the tangential velocity of a meteor orbiting the Earth? I have 2 expressions, not sure which is correct [closed]
"A meteoroid of mass $m$ is on a circular Earth orbit of radius $R$ which is a few (> 2) times larger than the radius of the Earth $R_E$. Derive an expression for the meteoroid's speed. State the ...
- 1,327
0
votes
1
answer
533
views
What does it mean to find an equation of motion, given vector functions that describe both the object's position and velocity?
I don't really understand how to approach a problem that asks to find the equation of motion. Intuitively, I would guess that an "equation of motion" is an equation where the particle's position is ...
- 1,179
0
votes
1
answer
4k
views
Two objects moving in the same direction; when do they meet? [closed]
I'm awful at physics and need help with a homework problem from my textbook. It reads as follows:
You are standing at rest at a bus stop. A bus moving at a constant speed of $5.00 \;\mathrm{m/s}$ ...
user129677
1
vote
1
answer
580
views
Projectile question doubt [closed]
A hunter wants to shoot a monkey with an arrow by launching the arrow at a speed $v_0$ at a distance of $L$ from the base of a tree of height $H$ on which the monkey is sitting. Now on watching the ...
user118752
1
vote
1
answer
1k
views
non constant acceleration problem [closed]
The acceleration of an arrow from a bow falls from $6000m/s^2$ to zero when it leaves the bow after travelling a distance $x=0.75m$. Assuming that this acceleration can be expressed by the linear ...
3
votes
1
answer
1k
views
finding velocity along a curve with kinematic equations using time
(i'm "not" looking for coding help. i need help setting up the math.)
i'm writing a program for a physics class to find the velocity of an object across a random curve. where the only force acting on ...
- 31
1
vote
1
answer
781
views
Formula - Bounce height with respect to time
I'm trying to graph a bounce with respect to time. I have these formulas:
$\frac 12 mV_2^2 = mgH_2$
and
$H_2 = \frac{1}{2} \frac{V_2^2}{g}$
I will have a series of $H(t)$ formulas as I know how to ...
- 133
0
votes
0
answers
182
views
Particle Disintegration Range of Angles (Landau& Lifshitz)
In the particle disintegration problem in the book by Landau and Lifshitz (pg 44 question 3), it is asked to find the range for $\theta=\theta_1+\theta_2$, where $\theta_1$ and $\theta_2$ are the ...
- 109
2
votes
2
answers
8k
views
Half-atwood machine with accelerating pulley
This is a follow-up to my previous question, in which I am now trying to calculate the acceleration of the cart (as before, the block surfaces are frictionless). The mass $m_2$ is attached to $M$ via ...
- 1,605
0
votes
2
answers
67
views
When considering the acceleration as constant? [closed]
I'm solving a simple dynamic exercise, exercise says:
"What is the absolute value of the force necessary to speed up a 500kg mass subject to 1600km/h in 1,8s, with the object from rest?"
Then I had ...
- 107
3
votes
2
answers
5k
views
Hockey puck collision [closed]
I have a homework question in which a sticky hockey puck traveling at constant velocity parallel to the side of the rink strikes a stationary puck and sticks to it. The angels between centres at ...
- 316
0
votes
1
answer
76
views
Questions about basic jump physics
This is a problem a friend and I are working on for an undergrad reading course. Our goal at the end is to make an accurate two-dimensional model of the human jump using Processing by the end of next ...
0
votes
2
answers
895
views
Finding the initial velocity of a vertical circular motion [closed]
A particle P is suspended from a fixed point O by a light inextensible string of length a. When hanging
at rest under gravity at A it is given a horizontal velocity u. The particle moves freely in a ...
- 135
0
votes
1
answer
266
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 moment ...
- 407
0
votes
1
answer
87
views
A pearl that moves in a smooth vertical hoop (Circular motion) [closed]
I couldn't understand something about the situation of a pearl that moves in a smooth vertical hoop in circular motion.
When the normal force equals 0 , the pearl didn't disconnect from the smooth ...
- 407
2
votes
4
answers
356
views
Acceleration and Circular Motion
Lets assume that there is a force that makes our body moves in circular motion.
We know that the acceleration of a body that moves in circular motion is Velocity ^ 2 / Radius .
How is it ...
- 407