a) The weight of the crate is 200 kg * 9.8 m/s^2 = <<200*9.8=1960>>1960 N.
b) The useful work done by the motor is the product of the force exerted by the motor and the distance through which it moves the crate. Since the weight of the crate is 1960 N and the motor raises it through a distance of 50 in, the useful work done by the motor is 1960 N * 0.42 m = 823.2 J.
c) The useful power of the motor is the useful work done by the motor divided by the time it takes to complete the work. Since the useful work done by the motor is 823.2 J and it takes 25 s to raise the crate, the useful power of the motor is 823.2 J / 25 s = 32.928 W.
d) The efficiency of the motor is the ratio of the useful power of the motor to the power it takes from its electricity supply. In this case, the efficiency of the motor is 32.928 W / 5000 W = 0.006585, or 0.6585%.