How much work should I be doing for A-level?

How much work is done by gravity on the two block system?

• A mass m1 = 6 kg rests on a frictionless table and connected by a massless string over a massless pulley to another mass m2 = 5.6 kg which hangs freely from the string. When released, the hanging mass falls a distance d = 0.79 m. 1. How much work is done by gravity on the two block system? 2. How much work is done by the Normal Force? 3. What is the final speed of the two blocks? 4. How much work is done by tension on m1? 5. What is the tension in the string as the ball falls? 6. The work done by tension on ONLY m2 is positive, zero, or negative? 7. What is the NET work done on m2? I realize this is a lot of work. You don't need to give me answers if you don't want to. I have a test coming up and I don't understand any of this, so I'd love it if someone could walk me through the problems. Thanks so much!

• Answer:

  1. The work done by gravity = m2*g*h = 5.6kg*9.8m/s^2*(0.79m) = 43.3J 2. Since the normal is perpendicular to the motion the work = 0 3. Use work-energy here so W = 1/2*(m1 + m2)*v^2 so v = sqrt(2*W/(m1 + m2)) = sqrt(2*43.3/(6+5.6)) = 2.73m/s 4.The work by tension on m1 = change in kinetic energy of m1 so W = 1/2*m1*v^2 = 1/2*6*2.73^2 = 22.4J 5. Since W = F*d then F (or tension) = W/d = 22.4/0.79 = 28.4N 6.Work done by tension on m2 is negative since the tension is up and the motion is down 7. Net work = answer from 1) = 43.3J