Question

A force of 20 N is required to pull up a body of mass 1.5 kg through a distance of 6 m along an inclined plane as shown in diagram alongside. Calculate

1. Force of gravity acting on the body. (Take g = 10 ms⁻²)
2. Work done by the force in pulling body along the inclined plane.
3. Work done against the force due to gravity
4. Account for the difference in answers (b) and (c).

Answer 1

(a) Force of gravity acting on the body = mg

= 1.5 kg × 10 ms⁻²

= 15 N

(b) Work done by the force in pulling body along inclined plane = Force × displacement

= 20 N × 6 m

= 120 J

(c) Work done against force of gravity = Force of gravity × vertical height 

= mg × BC

= mg × AC sin 30°

= \[ 15\ \mathrm{N} \times 6\ \mathrm{m} \times \frac{1}{2} \]

= 45 J

(d) The difference in work done (120 J – 45 J) = 75 J is the work done against the force of friction between the body and the inclined plane.