Fundamentals o Mechanics Final Exam 2011 Page 6 of 7 Questio

Fundamentals o Mechanics Final Exam 2011 Page 6 of 7 Question 9. (6 Marks) A box of mass 3 kg sits stationary on a rough surface. The co-effcients of friction between the box the surface are Ahorizontal 0.25 force of 6 N is applied to the box. what is the value of the friction force between the box and the surface? a) 8.83 N m 3kg b) 29.4 N c) 7.36 N 6N 6.0 N e) 18 N Question 10. (6 Marks) A box has a 100 N Force applied as shown. What is the magnitude of the moment of the force about the X axis? a) 618 Nm b) 450 Nm 300 Nm d) 424 Nm 00 Nm

Solution

9.normal reaction N = 3x9.81 = 29.43N

the friction force is Fn = 0.30 x 29.43 = 8.829 N > the applied force

so that the friction force is between the box and the surface = 6N

10. moment of the force in x-axis = force x perpendicular

= 3 x 100

= 300N-m