Final answer:
The force tending to lift the load off the ground when a boy pulls with a string inclined at 30° to the horizontal with a tension of 105 N is 52.5 N.
Step-by-step explanation:
The student asked about the force tending to lift a load off the ground when a boy is pulling with a string inclined at an angle to the horizontal. To solve this problem, we need to find the vertical component of the tension in the string, which is related to the force that tends to lift the load. Using trigonometry, we can find this vertical component by multiplying the tension by the sine of the angle (since it is the opposite side in a right-angled triangle).
The given tension in the string is 105 N and the angle is 30°. Using the sine function (sin 30° = 1/2), we can calculate the lifting force: F = T * sin(θ) = 105 N * 1/2 = 52.5 N.
Therefore, the force tending to lift the load off the ground is 52.5 N, which corresponds to option D.