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Pls answer the following problem and also give the detailed solution to it.

Pls answer the following problem and also give the detailed solution to it.

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Grade:11

1 Answers

Keren
21 Points
7 years ago
It is mentioned that the lift accelerated (moves upwards) and then decelerates (moves downwards)
Let the actual weight be: ‘M’ kg
Let the acceleration be: ‘a’ m/s2
 
(1) Acceleration
Given,
Max. weight: 72 kg
When the lift moves upwards, intertial force (pseudo force) movws downwards, adding to the weight of the person, thereby resulting in the 
‘maximum’ weight.
 
W = mg,
W = 72 x ‘g’ N,
where ‘g’ is the gravitational constant.
 
Now, the maximum weight should be equal to the apparent weight: mg+ma. (increase)
So,
 
72g = mg + ma ------ Equation 1
 
(2) Deceleration
Given,
Min. weight:  60 kg
When the lift moves downwards, inertial force (pseudo force) moves upwards, resulting in ‘minimum’ weight, thereby reducing the weight 
of the person.
 
W = mg,
W = 60 x ‘g’ N,
where ‘g’ is the gravitational constant.
Now, the minimum weight should be equal to apparent weight: mg-ma (decrease)
So,
 
60g = mg – ma -------Equation 2
 
 
Equation 1 + Equation 2 ----> 132g = mg +mg +ma -ma
                                           132g = 2mg
                                           m = 132/2 = 66kg
 
Actual weight: 66 kg
 
Equation 1 – Equation 2 ----> 72g – 60g = mg + ma -mg +ma
                                                    12g = 2ma
                                                     12 x 9.9 = 2 x 66 x a   ( g = 9.9 m/s2, 
                                                                                        m = 66kg)
                                                     9.9/11 = a
                                                    a = 0.9 m/s2
 
All the best!
 
Regards,
Keren ND,
Chennai. 
 
 

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