A 3-kg mass is attached to a vertical cord. (a) How muchtension in the cord is n

Question

A 3-kg mass is attached to a vertical cord. (a) How muchtension in the cord is needed to keep the mass moving upward at theconstant velocity 5 m/s? Calculate the acceleration if the tensionis (b) 42 N, (c) 24 N.(d) how much tension acting for 2 seconds isneeded to give the mass the upward velocity 12 m/s if it isinitially stationally? The question i was totally confused. When asked on thehomework, i got this question wrong. i didnt know how to work onthe problem. Please help, i know something similar like this willbe on the mid-term, i don't want to make the same mistake on themid-term. A 3-kg mass is attached to a vertical cord. (a) How muchtension in the cord is needed to keep the mass moving upward at theconstant velocity 5 m/s? Calculate the acceleration if the tensionis (b) 42 N, (c) 24 N.(d) how much tension acting for 2 seconds isneeded to give the mass the upward velocity 12 m/s if it isinitially stationally? The question i was totally confused. When asked on thehomework, i got this question wrong. i didnt know how to work onthe problem. Please help, i know something similar like this willbe on the mid-term, i don't want to make the same mistake on themid-term.

Explanation / Answer

   mass, m = 3 kg    Tension, T = mg + ma = m ( g + a ) (a)   T = m ( g + a ) = 3 ( 9.8 + 0 ) = 29.4N   ( here a = 0 because velocity is constant ) (b)   a = ( T - mg ) / m = [ 42 - ( 3 *9.8 ) ] / 3 = 4.2 m/s^2 (c)   a = ( T - mg ) / m = [ 24 - ( 3* 9.8 ) ] / 3 = - 1.8 m/s^2 (d)   a = v / t = 12 / 2 = 6 m/s^2          T = m (g + a) = 3 ( 9.8 + 6 ) = 47.4 N

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