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# Tag Archives: mechanics

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## How to do questions of mechanics efficiently?

How to do questions of mechanics efficiently???????????????????????
although hcv done but unable to solve new problems ………….hcv done with the help of solutions..help me

Sarthak  posted

We cannot just state all the tactics in a go, as the individual problems differ from each other and the techniques and tactics required are different.

However, these are some suggestions which will help you to solve the problems in Mechanics (and Physics in general)

• Visualize the problem.  You should be able to imagine and visualize the situation given in the problem. Draw diagrams to illustrate. Write in all the necessary details along with
• Write the physical quantities given, assumed and to be found using accepted notations. This will help you to zero in on the correct formula
• … To be continued

## Kinematics – Signs of displacement and Velocity

When will displacement and velocity be negative ? Can you explain me about angular acceleration and angular velocity.

[This question was asked via our mobile interface available at http://m.askphysics.com (mobile users visiting www.askphysics.com will be automatically redirected to the mobile version). We are happy that many of our visitors are using the mobile version and utilizing the facilities]

The signs are conventional. We take one direction as positive and the direction opposite to it as negative.

When we discuss one-dimensional motion, it is easy to take the help of the number-line, whatever towards right is positive and towards left is negative. If the initial direction of motion is taken as positive and the further displacements does not make the body to go beyond the initial position in opposite direction, the displacement will be positive.

## A thought provoking (HOTS) problem from rotation

Consider a disk rotating in a horizontal plane with a constant angular speed “omega” about its center O.

The disk has a shaded region on one side of the diameter and an unshaded region on the other  side.

When disk is in horizontal plane x-y with left half shaded and right half unshaded, two pebbles P and Q are simultaneously projected at an angle towards R.

The velocity of projection is in the y-z plane and is same for both pebbles with respect to the disk.

Assume that

(i) they land back on the disk before the disk has completed one-eighth rotation,

(ii) their range is less than half the disk  radius,and

(iii)”omega” remains constant throughout.

Then where will the two pebbles land?

(All are invited to answer this)

## Uniform Circular Motion in Horizontal Plane

In uniform horizontal circular motion, how are the vertical forces balanced?

If you are considering an object tied to a string and whirled with uniform speed in a horizontal plane, the object will be moving in a horizontal plane but the string has to make a certain angle with the horizontal so that the tension can be resolved in such a way that the horizontal component provides the centripetal force and the vertical component balances the weight of the body.

The motion will become almost entirely in a horizontal plane when the centripetal force is much larger than the weight of the particle.

Refer:

http://cnx.org/content/m14090/latest/

The case of rid body structures the situation is complex, but as long as there are no vertical accelerations, the vertical components of  forces will be balanced.

Comments are welcome from students and teachers WHO THINK!

## What is pseudo force

What is pseudo force when it is applied ?

Pseudo force is also called fictitious force.

A fictitious force arises when a frame of reference is accelerating compared to a non-accelerating frame.

For example if you consider a person standing at a bus stop watching an accelerating car, he infers that a force is exerted on the car and it is accelerating. Here there is no problem and the pseudoforce concept is not required

But, if the person inside the accelerating car is looking at the person standing at the bus stop, he finds (more…)

## A Problem from power

The power output of a machine that lifts a 600 kg
weight through a height of 20m in 1min is:
@)1.96kW    b)0.98kW

c)12kW      d)3.92kW”

Use the formula power = work /time

$P = \frac{mgh}{t}$

## More Problems from Kinematics

1. “On a 120 km track, a train moves the first 30 km at a uniform speed of 30 km/h. How fast must the train in the next 90 km so as to have average speed 60 km/h for the entire trip?”
2. “A person goes form one place to another on bike
with uniform speed 40 km/h and returns back at
uniform speed of 60 km/h. Find average speed
during the journey.”