Archive for April 2014

Gravitation: (May - June 2003 Paper 1 Question No. 03 )

Posted on Wednesday, April 30, 2014 by Nazmul Opu

On the Earth, the gravitational field strength is 10 N/kg. On the Moon, the gravitational field strength is 1.6 N/kg.

If an object has a weight of 50 N on Earth, what is its weight on the Moon?

A      1.6 N           
B      5.0 N            
C      8.0 N            
D      80 N

Correct Answer:  C (8.0 N)

Explanation: 

Here given,
            Gravitational field strength on Earth,  ge = 10 N/kg
            Gravitational field strength on Moon, gm = 1.6 N/kg
            If we suppose the mass as m kg, then

Weight on earth = mge
            50 N     = m kg x 10 N/kg
              m       = (50/10) kg = 5 kg

Now, weight on Moon = mgm
                                  = 5 kg x 1.6 N/kg
                                  = 8.0 N

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Gravitation: (May - June 2003 Paper 1 Question No. 02)

by Nazmul Opu




 An object is falling under gravity with terminal velocity.

What is happening to its speed?

A       It is decreasing to a lower value.

B       It is decreasing to zero.

C       It is increasing.

D       It is staying constant.


Correct Answer: D (It is staying constant)


Explanation: When an object starts falling under gravity its velocity increases due to gravitational acceleration but it also decreases gradually due to air resistance. At a point of time the air resistance becomes equal to the gravitational force. At this stage we say that the object reached its terminal velocity. As the air resistance and gravitational force both are cancelled by each other, the object has no acceleration and speed or velocity remains constant for the rest of the time. This is why droplets of water from rain fall from a very high altitude but do not strike heavily on the ground.

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Vernier Scale: (May - June 2003 Paper 1 Question No. 01)

by Nazmul Opu

The diagram shows part of a vernier scale.




What is the reading on the vernier scale?

A       6.50 cm

B       6.55 cm

C       7.00 cm

D       7.45 cm


Correct Answer: B (6.55 cm)

Explanation: We know that in vernier calipers there is a small scale called vernier scale. In most of the vernier scales there are 10 divisions marked from 0 to 10. In some other scales there are 20 divisions. Vernier constant is the measure of accuracy level of a vernier scale. The formula to find vernier constant is: 

Vernier Constant (V.C) = (1 / No. of divisions)

So, If the no. of divisions are 10 then the scale can measure up to (1/10) = 0.1 mm accurately and if there are 20 divisions then (1/20) = 0.05 mm is the accuracy level of the scale. As vernier constant is a ratio, it does not have any unit. Now to find the reading we have to add main scale reading with vernier scale reading. To find vernier scale reading you have to multiply the vernier scale reading with vernier constant and the value you will get will be in millimeters. So the work out is as follows:

Reading = Main Scale Reading + (Vernier Scale reading x vernier constant)
            = 6.5 cm + (5 x 0.1) mm
            = 6.5 cm + 0.05 cm
            = 6.55 cm

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