A 20kg mass is to be pulled up a slope inclined at 30o to the horizontal. If the efficiency of the plane is 75%, the force required to pull the load up the ...

To find the force required to pull the 20kg mass up a slope inclined at 30 degrees to the horizontal, we need to consider the weight of the object and the force needed to overcome friction. The weight of the object is given by the formula W = mg, where m is the mass and g is the acceleration due to gravity (10 m/s^2). So, W = 20 kg x 10 m/s^2 = 200 N. To find the force needed to overcome friction, we need to use the formula F = μN, where μ is the coefficient of friction and N is the normal force. The normal force is the component of the weight that is perpendicular to the slope, which is given by N = W cosθ, where θ is the angle of inclination (30 degrees in this case). So, N = 200 N x cos30 = 173.2 N. Assuming an efficiency of 75%, we know that only 75% of the force applied will go towards moving the object up the slope, while the rest will be lost to friction and other factors. So, the force required to pull the load up the plane is F = (1/0.75) x (200 N x sin30 + μN) = 266.67 N. Therefore, the answer is 266.67 N, which is closest to option C (133.3N).