Question

A person has a choice while trying to push a create across a horizontal pad of concrete: push it at a down-ward angle of 30 degrees, or pull it at the an upward angle of 30 degrees.

a) which choice is most likely to require less force on the part of the person?

1) pushing at the downward angle; 2) pulling it at the same angle, but upward; 3) pushing or pulling should not matter?

b) if he create has a mass of 50.0 kg and the coefficient of kinetic friction between it and the concrete is 0.750, calculate the required force to move it across the concrete at the steady speed for both situation ( solve this section and bring the solution for part b to the class for further discussion)

Answer 1

here,

a)

theta = 30 degree

2)

pulling it at the same angle requires less force

as the normal reaction force decreases and the frictional force decreases

b)

mass , m = 50 kg

uk = 0.75

when the force is upwards

for steady speed

F * cos(theta) = uk * N = uk * ( m * g - F * sin(theta)

F * cos(30) = 0.75 * ( 50 * 9.8 - F * sin(30))

F = 296.13 N

the force required is 296.13 N

when the force is upwards

for steady speed

F * cos(theta) = uk * N = uk * ( m * g + F * sin(theta)

F * cos(30) = 0.75 * ( 50 * 9.8 + F * sin(30))

F = 748.43 N

the force required is 748.43 N