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2.10 Application of force

There are a few problem involving F=ma and W=mg, both are describing the force.

Example  1               

Figure shows an object of mass  is placed on  a table.

                                 clip_image001

Calculate

(a)  the weight of the object

(b)     the normal reaction which is acting upwards from the table to the

 

Solution

 

 

 

 

Pulley System

 

Example 2

 

Figure shows a force ,P pulls a load of mass 4 kg by means a smooth pulley.

            clip_image003

               

                Determine the value of P if the load moves with

                (a)           an uniform velocity

                (b)           an acceleration of 2 ms-2.

 

Solution

 

 

 

 

 

 

Example 3

 

Figure shows two weights of mass 2 kg and 6 kg are joined by a length of rope passes over a smooth pulley.

              clip_image005

                If the system is released from rest, what is the

                (a)           tension of the rope

                (b)           acceleration of the weights?

 

Solution

 

 

 

 

 

 

 

Example 4

Figure shows a trolley of mass 2 kg is placed on the surface of a table.

             clip_image007

What is the acceleration of the trolley and the tension of the rope when the 3- kg weight is released if the surface of the table is

           (a)           smooth

          (b)           rough and has the frictional force 4 N.

 

Solution

 

 

 

 

Lift 

   

Situation

Equation

Conclusion

clip_image009

At rest

 

 

clip_image011

Moving up with uniform velocity

 

 

clip_image013

Moving up with acceleration

 

 

clip_image015

Moving up with deceleration

 

 

clip_image017

Moving down  with uniform velocity

 

 

clip_image019

Moving down with acceleration

 

 

clip_image021

Moving down with deceleration

 

 

clip_image023

Cable of lift breaks causing the lift to free fall

 

 

 

Example 5

 

A student of mass 50 kg stands on a weighing scale in a lift. What is the reading of the weighing scale if  the lift

(a)           at rest

(b)           moving up with an uniform velocity 20 ms-1

(c)            moving up with an acceleration 4 ms-2

(d)      moving up with a  deceleration 2 ms-2

(e)           moving down with an uniform velocity 30 ms-1

(f)             moving down an acceleration 5 ms-2

(g)            moving down with a  deceleration 3 ms-2

(h)           is free falling

 

Solution

 

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