question_answer

A boy of mass 50 kg is standing on a weighing machine placed at the floor of a lift. The machine reads his weight in newtons. What is the reading of the machine, if the lift is moving Upwards with a uniform Speed of \[10\text{ }m{{s}^{-1}}.\] \[(g=10m{{s}^{-2}})\]

A)  510 N                                   

B)  480 N

C)   490 N                                  

D)  500 N

Correct Answer: D

Solution :

 Given that mass of boy m = 50 kg Weighing machine is moving upwards with  uniform speed, so acceleration of machine will be zero, a = 0.                                       \[T-mg=ma\] \[T-50g=50\times a\] but         \[a=0\] \[T=50\,g\] \[T=50\times 10\] \[T=500\,N\]