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Angle between velocity and acceleration

Discuss a circumstance in which angle between velocity and acceleration is less than 90.

Discuss a circumstance in which angle between velocity and acceleration lies batween 180 and 90.

(Hifsa Zafar asked this)

Answer:

In projectile motion when the object is moving up, the angle between velocity and acceleration (due to gravity g) is between 90 degree and 180 degree.

during the downward motion of a projectile, the angle between velocity and acceleration is between 0 and 90 degree.

Kinematics Numerical

  1. A particle travels 20 m in 7th second and 24m in 9th sec. find initial velocity?
  2. in a projectile motion , a body thrown from the ground ,at what angle both the vertical height and range will be equal?
  3. The velocity v(cm/s) of a particle is given in terms of time t(in seconds) by the equation v = at+b/t+c. Dimension of a,b, and c are ?

A Problem from Projectile motion

“A ball  is projected vertically  upwards  with  an initial  velocity of 28m/s and is observed  to pass a  point  30m above  the  projection point,at what  2times does  the ball  pass these  points?”

(Vimal Raj Answered)


ans : 1.356 sec and 1.444 sec .
sol:
from v=u+at we get t=2.8 . (time taken to reach the max height )
fm v2-u2=2aS we get S=39.2 m (max height reached)
observer at 30 m .
so , in btw distance btw observer and ball (at the top) =9.2 m
at top ball is at rest and time taken to reach the observer can be calculaed from S=ut + 1/2 at2 ,we get t=1.356s .
and next time can be calculated by 2.8 – 1.356 =1.444 sec .

(The answer has not been scrutinized. If any error, teachers and visitors can post as comment)

Projectile Motion

Ramesh Asks:

“A body is projected with velocity u with an angle with the horizontal. What is its average velocity when it crosses half of its max height”

A numerical from Projectile motion, friction and more

Hale asked:

One side of the roof of a building slopes up at 33.5°. A roofer kicks a round, flat rock that has been thrown onto the roof by a neighborhood child. The rock slides straight up the incline with an initial speed of 15.0 m/s. The coefficient of kinetic friction between the rock and the roof is 0.430. The rock slides 10.0 m up the roof to its peak. It crosses the ridge and goes into free fall, following a parabolic trajectory above the far side of the roof, with negligible air resistance. Determine the maximum height the rock reaches above the point where it was kicked.

(The question is left for visitors to answer.)

Learn Physics Through Videos (Khan Academy)

One-dimensional motion

In this tutorial we begin to explore ideas of velocity and acceleration. We do exciting things like throw things off cliffs (far safer on paper than in real life) and see how high a ball will fly in the air.

Two-dimensional motion

You understand velocity and acceleration well in one-dimension. Now we can explore scenarios that are even more fun. With a little bit of trigonometry (you might want to review your basic trig, especially what sin and cos are), we can think about whether a baseball can clear the “green monster” at Fenway Park.

Forces and Newton’s laws of motion

This is the meat of much of classical physics. We think about what a force is and how Newton changed the world’s (and possibly your) view of how reality works.

Work and energy

“Energy” is a word that’s used a lot. Here, you’ll learn about how it’s one of the most useful concepts in physics. Along the way, we’ll talk about work, kinetic energy, potential energy, conservation of energy, and mechanical advantage.

Impacts and linear momentum

Momentum ties velocity and mass into one quantity. It might not be obvious why this is useful, but momentum has this cool property where the total amount of it never changes. This is called the conservation of momentum, and we can use it to analyze collisions and other interactions. Bam!

Moments, torque, and angular momentum

Everything you’ve learned about motion, forces, energy, and momentum can be reused to analyze rotating objects. There are some differences, though. Here, you’ll learn about rotational motion, moments, torque, and angular momentum.

Gravitation

Gravity is the force of attraction between masses. It’s the thing that pulls you down to earth. Here, you’ll learn precise meanings of the words mass and weight, and you’ll also learn how gravity affects falling near earth and orbits in space.

Oscillatory motion

Pendulums. Slinkies. You when you have to use the bathroom but it is occupied. These all go back and forth over and over and over again. This tutorial explores this type of motion.

Fluids

Atmospheric pressure is like an invisible friend who is always squeezing you with a big hug. Learn more about pressure, buoyant force, and flowing fluid so you can appreciate the sometimes invisible, but crucial, effect they have on us and the world around us.

Thermodynamics

Heat can be useful, but it can also be annoying. Understanding heat and the flow of heat allows us to build heat sinks that prevent our computers from overheating, build better engines, and prevent freeway overpasses from cracking.

Electric charge, electric force, and voltage

Electric forces hold together the atoms and molecules in your eyes which allow you to read this sentence. Take a moment and learn about the force that holds our bodies together.

Circuits

Circuits make computers, digital cameras, and video games possible. Circuits are driving an unprecedented rate of change in how we live. In this topic you’ll learn about the physics behind the electronic devices we use.

Magnetic forces and magnetic fields

The magnetic field of the Earth shields us from harmful radiation from the Sun. Magnetic fields also allow us to diagnose medical problems using an MRI. In this topic you’ll learn about the force and field that makes this possible.

Magnetic flux and Faraday’s law

Faraday’s law is how we get electrical power from most power plants and hydroelectric dams. Learn how magnetic flux allows us to turn the mechanical energy of falling water through a dam into electrical energy.

Mechanical waves and sound

Waves are responsible for basically every form of communication we use. Whether you’re talking out loud, texting on your phone, or waving to someone in a crowd there’s going to be a wave transmitting information. Learn about the basics of waves in this topic, then learn more about light waves in the topics below.

Light waves

Light can seem mysterious. What is light made out of? What causes color? How do 3D movies work? Learn about some of the mysterious properties of light in these tutorials.

Geometric optics

Light waves can be bent and reflected to form new and sometimes altered images. Understanding how light rays can be manipulated allows us to create better contact lenses, fiber optic cables, and high powered telescopes.

Special relativity (sneak peek)

Think you know about time and space? Think again. Einstein basically did a pile driver on all our brains when he came up with his theory of special relativity. Note: This topic is under construction. More videos and materials will be added soon.

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