Answer to Question #164290 in Physics for Andu

Question

6. Knowing that F1 = 10 N, d1 = 8 cm, F2 = 8 N and d2 = 5 cm, determine: a) Which of the moments is the most big, hourly or counterclockwise moment? b) Will the disk be in equilibrium? Why ? c) In which direction will the disk rotate, clockwise or counterclockwise?

Answer 1

a) The moments (torque) are given as follows:

$$\tau_1 = F_1d_1 = 10N\cdot 0.08m = 0.8\space N\cdot m\\ \tau_2 = F_2d_2 = 8N\cdot 0.05m = 0.4\space N\cdot m$$

Thus, the first one is the most big.

b) Assuming that these moments are applied in opposite directions, the disk will not be in equilibrium. The nessesary condition for a body to be in equilibrium is the following: sum of all moments applied to it should be zero. Since $\tau_1>\tau_2$, this is not the case in this problem.

c) Since $\tau_1>\tau_2$, disk will rotate in the direction the force $F_1$ pulls it.

Answer. a) $\tau_1$, d) No, c) in the direction of force $F_1$.