Question

Im trying to figure out how to do these three questions, im not positive of the formulas and cant find them in my notes. I did come up with an answer for number 20. but im not positive if i worked thru it right or not. i converted N to lbs (8) then got an answer of 7.4 seconds, if thats right please let me know, if it isnt maybe you can help me with where i may have gone wrong.

Thanks in advance for any help!

  

18) Consider the figure below. The box has a mass of done by the tension in the cord if tension is varied linealry from point A to point B 21 2o K3 2.5* 19) Consider figure below. If mass A drops 2 meters, what would the kinetic energy of block B equal to? Put your answer here. Kinetic Energy of blockB 20) Consider figure below. How long will it take for block A, weight 34 N, to come to rest? 5 Put down your ansmer here

Answer 1

Work done by tension is zero because at one end it does positive work and at other end it does negative so, if block a ve 2m then block B will more 6m. therefore If speed of A is v, speed of B is 3v for A, By energy conservation mg(2) = 1/2 mv^2 v = squareroot 4g m/s therefore speed of B = 3v = 3 squareroot 4g m/s kinetic energy = 1/2 mv^2 \r\n = 1/2 times 4 times 9 times 4 times 9.8 K.E = 705.6 Joules w = 34N w times 8/squareroot 8^2 + 15^2 = 8w/17 f = mu times w times 15/squareroot 8^2 + 15 f = 0.6 times w times 15/17 = 9w/17 Net force = f - 8w/17 = 9w/17 - 8w/17 f_net = w/17 therefore a = 34/17 times 9.8 = 2/9.8 m/s^2 a = 0.2041 m/s^2 u = 15 m/s v = u + at 0 = 15 - 0.2041 t t = 73.5 seconds