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# Tag Archives: Automobile

## A spring is held vertically downward and a current is passed through it . Then the length of the spring :

A spring is held vertically downward and a current is passed through it . Then the length of the spring :

A . increases     B. decreases    C . does not change    D the spring oscillates

Since the adjacent turns are carrying currents in the same direction (just like two parallel wires) there will be attraction between the turns and therefore the length of the spring

tends to decrease.

## Problems from Electricity

1. The parallel plates of an air filled capacitor with area of area 1.1 x 10^8 m^2 . What must be the width of the plate be if the Capacitance is 1 Farad?
2. Four capacitor each of 2microfarad are connected in such a way that total capacitance is also 2microfarad. Show what combination gives this value. Also try to illustrate the diagram.

(Fari posted these)

1.Using the formula: $C=&space;A\varepsilon&space;/d$

and substituting , C= 1 F, A = 1.1 x 108, $\varepsilon$ = 8.8 x 10-12,

we get  , d =9.68×10-4 metres

2.

## Relative motion – Problem

A driving instructor tells his student to maintain a 3 second separation between the students car and the car ahead.

Suppose the cars are traveling 25m/s. How many meters apart are the cars? If the trailing car brakes at 9m/s^2 how much distance is required to stop?

Get more such problems here and here

a) 75 m

b)

## Numerical from Laws of Motion

Two cars a and b are moving towards each other on horizontal surface.the car a has mass 60 kg and moves towards the right with speed 60 m/s.the car b has mass 1000 kg and move towards the left with a speed 20m/sec.the two car collide and get stuck to each other.with what velocity will they move after collision