Physics 9702 · AS & A Level · Equilibrium of forces
Equilibrium of forces — practice question
A block is dragged across a horizontal surface by a force $P$, as illustrated in Fig. 4.1. The block has a weight of $180\text{ N}$. The force $P$ is $35\text{ N}$ at $60^\circ$ to the vertical. The block travels a distance of $20\text{ m}$ at constant velocity.
(a(i))[2]
Calculate the vertical force exerted by the surface on the block (normal reaction force).
(a(ii))[2]
Calculate the work done by force $P$ on the block.
(b(i))[1]
Explain why the block keeps moving at constant velocity even though work is done on it by force $P$.
(b(ii))[2]
Explain, in terms of the forces on the block, why it remains in equilibrium.
Worked solution & mark scheme
This 7-mark question has a full step-by-step worked solution and mark scheme. One marking point: “vertical reaction force $= $ weight $- P\cos60^\circ = 180 - 35\cos60^\circ = 160\ (163)\ \mathrm{N}$” …