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# Tag Archives: distance

## Why direct currents aren’t used in Home circuits?

How can an alternating current change its direction while moving in a wire or any conductor? Why direct currents aren’t used in Home circuits?

RAHUL ASKED

Answer:

Alternating current is produced by rotating a coil in a strong magnetic field (or by rotating magnet around the coil)

So, during every half rotation the direction of emf (voltage) induced in the coil reverses and hence the current too reverses its direction. The frequency of ac in India is 50 Hz and therefore in every 1 sec there will be 100 changes in direction.

Alternating currents are suitable for long distance as it can be stepped up using transformer to minimize energy loss and can be stepped down for use at home.

## Problem from relative velocity

A Boat covers certain distance between two spots in a river taking t1 hrs going downstream and t2 hrs going upstream. What time will be taken by boat to cover same distance in still water?

posted by STUTI

Answer:

## The problem of a rock thrown vertically up

**A rock is thrown vertically upward from the ground with an initial speed 15m/s.**

**a. how high does it go b. how much time is required for the rock to reach its maximum height? c. what is the rock’s height at t=2.00s?**

*(Posted by Merhawi)*

**Answer:**

(a)

u=15m/s

a=-10m/s^{2}

v=0 m/s (at the max height)

S=?

v^{2}-u^{2}=2aS

S=v^{2}-u^{2}/2a

=225/20

**=11.25 m**

(b) From the above case

using v=u+at

t=v-u/a=**1.5s**

(c) Use S = ut + 1/2 at^{2}

put t=2s, u = 15m/s, a=-10m/s^{2}

S=30 – 20 = **10 m**

*(If you use g = 9.8 m/s ^{2 }The answers will be slightly different)*

## Solution to HC Verma Problem

“Referring to HC Verma Part 2, chapter 29, Electric field and potential, Q 69

I think that Force is inversely proportional to square of the distance between the charged particles, so acceleration is not constant and hence

v*v = u*u + 2*a*s is not valid in this case.

How is proceed with this question ?” Satyam asked

## The question of minimum time and minimum distance in crossing a river.

A man crosses a river in a boat if he crosses the river in minimum time he take 10min with a drift 120metre if he crosses the river taking shortest path he takes 12.5min find the width of the river

## Tossing a coin in a moving train.

if a man tossed a coin in a moving train and the coin fell back then in which type if motion train is moving? and how?

Answer: This shows that the train is accelerated. When the coin was thrown, it had the same velocity of the train. If the train was not accelerated, the coin would have fallen on to the hands of the man itself. But the accelerated train moves a greater horizontal distance than by the coin.

## Problems from Kinematics again!

- Two bodies one held 40 m above other, are released simultaneously . After falling for 3 sec under gravity, their relative separation is?
- A particle covers half the distance between two points for equal time for

V1 and V2 and other half with V3 and V4 for equal distance. find average

velocity?

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