A cord is used to lower a block of mass 'M' and moves a distance 'd' with constant acceleration 'g/4'. Calculate the work done by the cord on the block.
 
 

Asked by aarya_t | 26th Feb, 2015, 10:16: PM

Expert Answer:

When the block is lowered, it experiences an upward force T due to tension and the net force on the block in the downward direction reduces from Mg to Mg-T. Hence the acceleration 'a' becomes less than 'g'. 
 
Equation of motion:
Mg - T = Ma
 
Given, a = g/4
begin mathsize 14px style therefore end styleT=3 Mg/4
Work done by the tension,
begin mathsize 14px style straight W space equals space straight T space straight d space cos space 180 to the power of straight o space space space space equals negative 3 over 4 Mg space straight d end style

Answered by Faiza Lambe | 27th Feb, 2015, 09:14: AM