In Fig. 4.9, two blocks are connected by a string, as shown, and the upper block is pulled upward by a different string. The masses of the upper and lower blocks are 300 grams and 240 grams, respectively. The string between the blocks will break if its tension exceeds 3.6 N, and the string that pulls the combination upward will break if its tension exceeds 7.8 N. (a) What is the largest upward acceleration that the blocks can be given without either string breaking? (Take g = 9.8 m/s2.) If the upward acceleration is slightly higher than this, which string breaks?
Explanation / Answer
max acceleration for T=7.8 N a=7.8/(0.3+0.24)=14.44 m/s2 for T=3.6 N => a'=3.6/0.24=15 m/s2 >a => maximum value of acceleration =14.44 m/s2 (b) if acceleraton exceeds above value, the lower string willbe broken. (b) if acceleraton exceeds above value, the lower string willbe broken.