Question

Jack and Jill lift upward on a 1.3kg pail of water. Jack exerts a force of 7.0N and Jill exerts a force of 11N. Jill’s force is exerted at an angle of 28º with the vertical. At what angle should Jack’s force be if the pail is accelerated straight upward?

Answer 1

1) The minimum vertical upward force has to be slightly greater than the weight of the pail of water.

2) Weight of the pail of water = mass * g = 1.3 kg * 9.8 m/s^2 = 12.74 N

3) Jill's upward vertical force = 11.0N cos(28°) = 9.71 N

4) Jack's upward vertical force = 7.0N cos (x)

5) Net upward vertical force = weight of the pail of water

=> 9.71N + 7.0N cos(x) = 12.74N

=> cos(x) = [12.74 N - 9.71N ] / (7.0 N) = 0.4329

6) x = arc cos(0.4329) = 64.4°

Answer: 64.4° with the vertical