### Why a cricketer lowers his hands while catching a ball?

• We know how to calculate the kinetic energy of moving objects -- isn't that enough? No. It turns out that many situations involving collisions do not obey the simple conservation of Mechanical Energy. Why not? Because it takes energy to bend, break, mutilate and deform objects, energy which disappears from the kinetic and gravitational potential energy.

• But a different quantity is conserved, even during collisions. The linear momentum of an object is defined as
```                   p  =  (mass) * (velocity)
```
It is a vector quantity, and the total linear momentum of a bunch of objects will remain the same, before and after a collision.

• Momentum is connected to force by impulse, which is simply
```            impulse   =  (force) * (time)
```
if the force has a constant magnitude during its action. If the force changes with time, then one must integrate to find the impulse:
```                         /
impulse   =  |  (force) dt```
```                         /
```

• The Momentum-Impulse Theorem states that the change in momentum of an object is equal to the impulse exerted on it:
```           (change in momentum)    =  (impulse)

p      -   p          =  (force) * (time)
final      initial

m*v      -  m*v         =  (force) * (time)
final       initial```

Impulse  It is effect of force acting for a short interval of time.
According to Newton’s 2nd law
Rate of change of momentum = Force applied.
If time period dt is  increased than Impact force decreases.

Why a cricketer lowers his hands while catching a ball

If suppose a 0.16 kg cricket ball hits a bat at 100 km/hr and then comes off the bat at 100 km/hr in 0.001 sec. The average force on ball is 8800 N which is enough to lift 880 kg of mass off the ground.  That is why it hurts to get struck by ball. Therefore while catching cricketer lowers his hands to increase time interval of change in momentum thereby impact force reduces and the chances of any injury and avoiding reaction of hand that can drop the catch .

### COMMON COLLECTOR CONFIGURATION OF A TRANSISTOR

COMMON COLLECTOR CONNECTION

In  this  configuration  the  input  is  applied  between the  base  and  the  collector and  the  output  is  taken  from  the  collector  and  the  emitter.  Here  the  collector  is common to both the input and the output circuits as shown in Fig.

Common Collector Transistor Circuit

In  common  collector  configuration  the  input  current  is  the  base current  IB  and  the output current is the emitter current IE. The ratio of change in emitter current to the  change in the base current is called current amplification factor.

It is represented by

COMMON COLLECTOR CIRCUIT

A test  circuit  for determining the  static characteristic  of an NPN transistor is shown in Fig. In this circuit the collector is common to both the input and the output circuits.   To   measure   the   base   and   the   emitter   currents,   milli   ammeters   are connected in series with the base and the emitter circuits. Voltmeters are connected   across the input an…