physics question related to motion . hurry plz help!?

Question

give an example for the following situations:-

a)a body with constant acceleration but with 0 velocity

b)an object moving in a certain direction with acceleration in the perpendicular direction.

Answer 1

a) a ball that was thrown upwards and has reached its peak height. it has momentarily stopped but gravity is still acting on it.

b) an ion in a magnetic field

Answer 2

anotherhumanmale has given very good answers, but on the second answer, I thought a bit of detail might be in order.

My first thought was of a bucket on a string, swinging it around in a circle. At any given time, the force, and thus the acceleration is perpendicular to the motion of the bucket.

Now the problem with this is, when you pick the bucket up, it's motion and acceleration are in the same direction, and if the rope loosens or slacks, then you also have slight motion which is not perpendicular to the force.

Likewise with the motion of the earth around the sun, for part of the year, part of our motion is toward the sun, and part is away. The earth is closer to the sun during the Australian summer than during the northern summer, for instance. So the acceleration of the earth toward the sun is almost, but not quite perpendicular to its motion.

However, in the case of the ion in the magnetic field, you have an infrastructural limitation on the direction of the force. Magnetic force can ONLY be applied perpendicular to the motion of the ion, because that is the very definition of the force. Either the Biot Savart Law or the Lorentz Force,

F = q v X B, where F=Force, q=charge of the ion, v=velocity, and B is the magnetic field. The X represents a cross product, meaning the force is perpendicular to both the magnetic field and the velocity of the ion.

In this way, magnetism affects a particles acceleration ONLY in a direction perpendicular to its motion, while gravity, tension, friction, etc. affect acceleration in different ways.

Well, I got carried away there, didn't I! Thanks for the question.

Answer 3

Well, let me see :

a) This one is easy, just imagine that you have thrown an object to the sky, and in the top of its movement, that object will have zero velocity, but it will have a constant acceleration, the acceleration of gravity, the velocity is 0, yes the final velocity is 0, but the acceleration is constant at that point.

b) Imagine you fire a bomb parallel to the ground, it is moving from left to right, but the gravity is acting on it, so the acceleration is perpendicular to the direction of the bomb, but the bomb is moving from left to right.

Hope it helps

Answer 4

A pendulum at either end of its swing, when momentarily at rest. The pendulum has come to a momentary halt but the acceleration due to gravity continues to act. Similarly the trapeze artist in a circus at the end of a swing etc.

b) earth is going around the sun and the acceleration is towards the centre, perpendicular to its direction of motion. Similarly, all circular motion involves same conditions.

Answer 5

a) constant acceleration and 0 velocity eh?
given that an object thrown upwards (even at the apex of its flight) still has the tangential velocity of the earth (earth rotates 24000 miles in 24 hours = 1000 mph) and given that the earth is traveling about 67,000 mph through space during it's orbit around the sun and God only knows how fast our solar system is traveling through our galaxy, etc, the object will ALWAYS have a velocity depending on how you're looking at it. The only way to answer this is in relativistic terms.

Think of your frame of reference. Say your in an airplane flying above the earth. And you place an object on your tray table. Say your mp3 player. The object has zero velocity relative to your frame of reference (the airplane) but yet has constant acceleration due to the earths gravity. It still has a velocity relative to an observer on the ground or to an observer in an oncoming airplane. But to you, it has zero velocity. Relativity.

b) A satellite in orbit. moves tangential to the earth. acceleration is perpendicular to it's motion.