Physics 9702 · AS & A Level · Equilibrium of forces

Equilibrium of forces — practice question

(a)[2]

State the two conditions that must be satisfied for a system to be in equilibrium.

(b)

A paraglider P of mass $95\,\text{kg}$ is towed by a wire attached to a boat, as shown in Fig. 2.1. The wire is inclined at $25^{\circ}$ to the horizontal water surface. P travels in a straight line parallel to the water surface. Fig. 2.2 shows how the velocity $v$ of P varies with time $t$.

(b(i))[2]

Show that the acceleration of P is $1.4\,\text{m s}^{-2}$ at time $t = 5.0\,\text{s}$.

(b(ii))[2]

Calculate the total distance travelled by P from $t = 0$ to $t = 7.0\,\text{s}$.

(b(iii))[2]

Calculate the change in kinetic energy of P from time $t = 0$ to $t = 7.0\,\text{s}$.

(b(iv).1)[3]

The tension in the wire at time $t = 5.0\,\text{s}$ is $280\,\text{N}$. For the horizontal motion, calculate the vertical lift force $F$ supporting P.

(b(iv).2)[3]

Calculate the force $R$ due to air resistance acting on P in the horizontal direction.

(c(i))[2]

Show that the acceleration of P is $1.4\,\text{m s}^{-2}$ at time $t = 5.0\,\text{s}$.

(c(ii))[2]

Calculate the total distance travelled by P from time $t = 0$ to $t = 7.0\,\text{s}$.

(c(iii))[2]

Calculate the change in kinetic energy of P from time $t = 0$ to $t = 7.0\,\text{s}$.

(c(iv)1)[3]

The tension in the wire at time $t = 5.0\,\text{s}$ is $280\,\text{N}$. For the horizontal motion, calculate the vertical lift force $F$ supporting P.

(c(iv)2)[3]

The tension in the wire at time $t = 5.0\,\text{s}$ is $280\,\text{N}$. For the horizontal motion, calculate the force $R$ due to air resistance acting on P in the horizontal direction.

Worked solution & mark scheme

This 26-mark question has a full step-by-step worked solution and mark scheme. One marking point: Resultant force in any direction is zero

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