A worker must move a crate that can be either pushed at a slight downward angle of 25° or pulled at a slight upward angle of 25° as shown in the diagrams. In both cases, the worker can exert a force of 360 N and the crate has a mass of 45 kg.
Calculate the acceleration of the crate in both situations, given that the coefficient of friction between the crate and the floor is 0.26. Explain the difference in accelerations that exists between the two situations.
If you are pulling upward the friction force is less
worker force in direction of motion
= 360 cos 25 = 326 Newtons (both cases)
Friction force:
Pushing down = 0.26( m g + 360 sin 25) = 0.26(45*9.81+152) = 154 N
Pulling up = 0.26 (m g - 360 sin 25) = 0.26(441 - 152) = 75.1 N
326 - 154 =172
326 - 75 = 251
a pushing downward = 172 / 45
a pulling upward = 251 / 45