Past Exam Questions

To find the tensions in the strings, we resolve the forces acting on the particle P vertically and horizontally.

Vertically, the sum of the vertical components of the tensions must equal the weight of the particle:

\(T_A \frac{1}{2.6} + T_B \frac{1}{1.25} = 10.5\)

Horizontally, the horizontal components of the tensions must balance each other:

\(T_A \frac{2.4}{2.6} = T_B \frac{0.75}{1.25}\)

Solving these equations simultaneously gives:

\(T_A = 6.5 \text{ N}\)

\(T_B = 10 \text{ N}\)

Given that \(\tan \alpha = \frac{8}{15}\), we can find \(\cos \alpha\) and \(\sin \alpha\) using the identity \(\tan \alpha = \frac{\sin \alpha}{\cos \alpha}\).

Let \(\sin \alpha = \frac{8}{17}\) and \(\cos \alpha = \frac{15}{17}\) based on the Pythagorean identity \(\sin^2 \alpha + \cos^2 \alpha = 1\).

Resolve forces vertically: \(T \cos \alpha = mg\).

Substitute \(\cos \alpha = \frac{15}{17}\) and \(mg = 0.3 \times 9.8 = 2.94\) N:

\(T \times \frac{15}{17} = 2.94\).

\(T = \frac{2.94 \times 17}{15} = 3.4\) N.

Resolve forces horizontally: \(F = T \sin \alpha\).

Substitute \(T = 3.4\) N and \(\sin \alpha = \frac{8}{17}\):

\(F = 3.4 \times \frac{8}{17} = 1.6\) N.

To solve for the tensions in the strings, we resolve the forces acting on P horizontally and vertically. Let the tension in PA be T_A and in PB be T_B.

Using the geometry of the triangle formed by the strings and the vertical line, we have:

\(T_A \times \frac{40}{50} + T_B \times \frac{40}{104} = 21\)

Solving for T_A and T_B:

\(T_A \times \frac{30}{50} = T_B \times \frac{96}{104}\)

From the first equation, we find:

\(T_A = 20 \text{ N}\)

Substituting T_A into the second equation gives:

\(T_B = 13 \text{ N}\)

Thus, the tension in AP is 20 N and the tension in BP is 13 N.

To solve for the tensions in the strings, we resolve the forces horizontally and vertically.

1. Resolve horizontally:

\(T_1 \cos 35^{\circ} = T_2 \cos 40^{\circ}\)

2. Resolve vertically:

\(T_1 \sin 35^{\circ} + T_2 \sin 40^{\circ} = 2.4g\)

where \(g\) is the acceleration due to gravity, approximately \(9.8 \text{ m/s}^2\).

3. Solve the system of equations:

From the horizontal resolution, express \(T_2\) in terms of \(T_1\):

\(T_2 = \frac{T_1 \cos 35^{\circ}}{\cos 40^{\circ}}\)

Substitute \(T_2\) in the vertical resolution equation:

\(T_1 \sin 35^{\circ} + \left(\frac{T_1 \cos 35^{\circ}}{\cos 40^{\circ}}\right) \sin 40^{\circ} = 2.4 \times 9.8\)

Simplify and solve for \(T_1\):

\(T_1 (\sin 35^{\circ} + \frac{\cos 35^{\circ} \sin 40^{\circ}}{\cos 40^{\circ}}) = 23.52\)

\(T_1 = \frac{23.52}{\sin 35^{\circ} + \frac{\cos 35^{\circ} \sin 40^{\circ}}{\cos 40^{\circ}}} \approx 20.4 \text{ N}\)

4. Substitute \(T_1\) back to find \(T_2\):

\(T_2 = \frac{20.4 \cos 35^{\circ}}{\cos 40^{\circ}} \approx 19.0 \text{ N}\)

To solve for the tensions in the strings, we can use the equilibrium conditions for the forces acting on the particle P. The forces involved are the tensions in the strings S₁ and S₂, and the weight of the particle.

Let the tension in S₁ be T₁ and in S₂ be T₂. The weight of the particle is 21 N acting vertically downward.

Using trigonometry, we can resolve the tensions into horizontal and vertical components. The horizontal components must balance each other, and the sum of the vertical components must balance the weight of the particle.

From the diagram, we can determine the angles using the given lengths:

• For S₁: \\(an^{-1}(0.2/0.52) = 21.8^\circ\\)
• For S₂: \\(an^{-1}(0.2/0.25) = 38.7^\circ\\)

Resolving horizontally:

\(T_1 \cos(21.8^\circ) = T_2 \cos(38.7^\circ)\)

Resolving vertically:

\(T_1 \sin(21.8^\circ) + T_2 \sin(38.7^\circ) = 21\)

Solving these equations simultaneously gives:

\(T_1 = 13\) N

\(T_2 = 20\) N

To find the angle AP₁X, we use the cosine rule in triangle XP₁A:

\(\cos \alpha = \frac{5.5}{7.3}\)

Solving for \(\alpha\), we get \(\alpha = 41.1^\circ\).

For the value of W, we use the sine rule in triangle XP₁C:

\(\frac{W}{\sin(180^\circ - 41.1^\circ)} = \frac{7.3}{\sin 90^\circ}\)

Solving for W, we find \(W = 4.8 \text{ N}\).

To solve for \(W_1\) and \(W_2\), we use the triangle of forces and the sine rule. The angles in the triangle are 40°, 60°, and 80°.

Using the sine rule:

\(\frac{W_1}{\sin 60^{\circ}} = \frac{5}{\sin 80^{\circ}}\)

Solving for \(W_1\):

\(W_1 = \frac{5 \cdot \sin 60^{\circ}}{\sin 80^{\circ}} = 4.40 \text{ N}\)

Similarly, for \(W_2\):

\(\frac{W_2}{\sin 40^{\circ}} = \frac{5}{\sin 80^{\circ}}\)

Solving for \(W_2\):

\(W_2 = \frac{5 \cdot \sin 40^{\circ}}{\sin 80^{\circ}} = 3.26 \text{ N}\)

(a) To find the magnitude of the force in each of the struts AD and BD, resolve vertically:

\(500 + T \cos 45^{\circ} + T \cos 45^{\circ} - 100g = 0\)

Since \(T_A = T_B = T\), we have:

\(500 + 2T \cos 45^{\circ} = 100g\)

Solving for \(T\):

\(T \cos 45^{\circ} = \frac{100g - 500}{2}\)

\(T = \frac{500}{\sqrt{2}} = 354 \text{ N}\)

(b) To find the value of \(F\) for which the magnitude of the force in the strut AD is zero, resolve horizontally and vertically:

Vertically:

\(T_B \cos 45^{\circ} + 500 - 100g = 0\)

Horizontally:

\(F - T_B \sin 45^{\circ} = 0\)

Solving for \(F\):

\(F = T_B \sin 45^{\circ}\)

Since \(T_B \cos 45^{\circ} = 100g - 500\),

\(T_B = \frac{100g - 500}{\cos 45^{\circ}}\)

\(F = \frac{100g - 500}{\cos 45^{\circ}} \sin 45^{\circ} = 500 \text{ N}\)

Let the tension in the string attached to the wall be \(T\).

Resolve forces horizontally:

\(T \cos \alpha = 4 \sin 60^{\circ}\)

Resolve forces vertically:

\(T \sin \alpha + 4 \cos 60^{\circ} = 0.3g\)

Substitute \(g = 9.8 \, \text{m/s}^2\):

\(T \sin \alpha + 4 \times 0.5 = 0.3 \times 9.8\)

\(T \sin \alpha = 2.94 - 2\)

\(T \sin \alpha = 0.94\)

Using the horizontal equation:

\(T \cos \alpha = 4 \times \frac{\sqrt{3}}{2}\)

\(T \cos \alpha = 2\sqrt{3}\)

Divide the two equations:

\(\tan \alpha = \frac{0.94}{2\sqrt{3}}\)

\(\alpha = \arctan \left( \frac{0.94}{2\sqrt{3}} \right) \approx 76.9^{\circ}\)

Substitute \(\alpha\) back to find \(T\):

\(T = \frac{2\sqrt{3}}{\cos 76.9^{\circ}} \approx 2.05 \text{ N}\)

To solve for the tensions in the strings, we resolve the forces horizontally and vertically.

Let the tensions in the strings be \(T_1\) and \(T_2\).

Resolving horizontally:

\(T_1 \cos 60^{\circ} = T_2 \cos 45^{\circ}\)

Resolving vertically:

\(T_1 \sin 60^{\circ} + T_2 \sin 45^{\circ} = 8g\)

Substituting \(g = 9.8 \text{ m/s}^2\), we have:

\(T_1 \cos 60^{\circ} = T_2 \cos 45^{\circ}\)

\(T_1 \sin 60^{\circ} + T_2 \sin 45^{\circ} = 8 \times 9.8\)

Solving these equations simultaneously gives:

\(T_1 = 58.6 \text{ N}\)

\(T_2 = 41.4 \text{ N}\)

An alternative method using Lami's Theorem:

\(\frac{T_1}{\sin 135^{\circ}} = \frac{T_2}{\sin 150^{\circ}} = \frac{80}{\sin 75^{\circ}}\)

Solving for \(T_1\) and \(T_2\) gives the same results:

\(T_1 = 58.6 \text{ N}\)

\(T_2 = 41.4 \text{ N}\)

(a) Resolve horizontally: \(100 - T_U \sin 60 - T_L \sin 60 = 0\)

Resolve vertically: \(T_U \cos 60 - T_L \cos 60 - 5g = 0\)

Perpendicular to \(T_U\): \(T_L \cos 30 + 5g \cos 30 = 100 \cos 60\)

Solve for \(T_L\): \(T_L = 7.74 \text{ N}\)

(b) Resolve horizontally: \(X - T_{up} \sin 60 = 0\)

Resolve vertically: \(T_{up} \cos 60 - 5g = 0\)

Perpendicular to \(T_{up}\): \(5g \cos 30 = X \cos 60\)

Eliminate \(T_{up}\) and solve for \(X\): Least value of \(X = 86.6\)

To find the tensions in the strings, resolve the forces horizontally and vertically.

Resolving horizontally:

\(T_P \cos 60^{\circ} = T_R \cos 30^{\circ}\)

Resolving vertically:

\(T_P \sin 60^{\circ} = T_R \sin 30^{\circ} + 0.2g\)

Using \(g = 9.8 \text{ m/s}^2\), solve these equations simultaneously.

From the horizontal resolution:

\(T_P \cdot 0.5 = T_R \cdot \frac{\sqrt{3}}{2}\)

\(T_P = T_R \cdot \sqrt{3}\)

Substitute \(T_P = T_R \cdot \sqrt{3}\) into the vertical resolution:

\(T_R \cdot \sqrt{3} \cdot \frac{\sqrt{3}}{2} = T_R \cdot 0.5 + 0.2 \cdot 9.8\)

\(\frac{3}{2} T_R = 0.5 T_R + 1.96\)

\(T_R = 2 \text{ N}\)

Substitute \(T_R = 2 \text{ N}\) back to find \(T_P\):

\(T_P = 2 \cdot \sqrt{3} \approx 3.46 \text{ N}\)

Resolve the forces horizontally:

\(20 \cos 60^\circ = T \cos 45^\circ\)

\(T = \frac{20 \cos 60^\circ}{\cos 45^\circ} = 10\sqrt{2}\) or 14.1 \text{ N}

Resolve the forces vertically:

\(20 \sin 60^\circ + T \sin 45^\circ = mg\)

\(m = \frac{20 \sin 60^\circ + T \sin 45^\circ}{g}\)

Substitute \(T = 10\sqrt{2}\):

\(m = \frac{20 \times \frac{\sqrt{3}}{2} + 10\sqrt{2} \times \frac{\sqrt{2}}{2}}{g} = 2.73 \text{ kg}\)

To solve for the tensions in the strings, we resolve the forces vertically and horizontally.

Vertically, the equilibrium condition gives:

\(T_A \times \frac{4}{5} + T_B \times \frac{3}{5} = 5\)

Horizontally, the equilibrium condition gives:

\(T_A \times \frac{3}{5} = T_B \times \frac{4}{5}\)

Solving these equations simultaneously, we find:

\(T_A = 1.6 \text{ N}\)

\(T_B = 1.2 \text{ N}\)

To solve for the tension \(T\) and the mass \(m\), we resolve forces horizontally and vertically.

Horizontally, the equilibrium condition gives:

\(T \sin 30^{\circ} + T \sin 40^{\circ} - 2 = 0\)

Vertically, the equilibrium condition gives:

\(T \cos 30^{\circ} - T \cos 40^{\circ} - mg = 0\)

Solving the horizontal equation for \(T\):

\(T (\sin 30^{\circ} + \sin 40^{\circ}) = 2\)

\(T = \frac{2}{\sin 30^{\circ} + \sin 40^{\circ}}\)

Substituting the values of \(\sin 30^{\circ} = 0.5\) and \(\sin 40^{\circ} \approx 0.6428\):

\(T = \frac{2}{0.5 + 0.6428} \approx 1.75\)

Substitute \(T = 1.75\) into the vertical equation:

\(1.75 \cos 30^{\circ} - 1.75 \cos 40^{\circ} = mg\)

\(mg = 1.75 (\cos 30^{\circ} - \cos 40^{\circ})\)

Using \(\cos 30^{\circ} \approx 0.866\) and \(\cos 40^{\circ} \approx 0.766\):

\(mg = 1.75 (0.866 - 0.766)\)

\(mg = 1.75 \times 0.1 = 0.175\)

\(m = \frac{0.175}{g}\)

Assuming \(g = 9.8\):

\(m \approx \frac{0.175}{9.8} \approx 0.0175\)

To solve for the tension in the string and the value of X, we resolve the forces acting on the ring R.

1. Resolve vertically: \(X \sin 60^{\circ} + T \sin 30^{\circ} - 0.2g = 0\)

2. Resolve horizontally: \(X \cos 60^{\circ} - T - T \cos 30^{\circ} = 0\)

Solving these equations simultaneously:

From the vertical resolution, substitute the known values: \(X \cdot \frac{\sqrt{3}}{2} + T \cdot \frac{1}{2} = 0.2 \cdot 9.8\)

From the horizontal resolution: \(X \cdot \frac{1}{2} = T + T \cdot \frac{\sqrt{3}}{2}\)

Solving these equations gives: \(X = 2\) \(T = 0.536 \text{ N}\)

To solve this problem, we need to resolve the forces acting on the ring R both vertically and horizontally.

Vertically: The vertical components of the tension must balance the weight of the ring. The weight of the ring is given by:

\(0.2g\)

where \(g\) is the acceleration due to gravity (approximately 9.8 m/s²). The vertical components of the tension are:

\(T \sin 70^{\circ} + T \sin 45^{\circ} = 0.2g\)

Solving for \(T\):

\(T(\sin 70^{\circ} + \sin 45^{\circ}) = 0.2 \times 9.8\)

\(T = \frac{0.2 \times 9.8}{\sin 70^{\circ} + \sin 45^{\circ}} \approx 1.21 \text{ N}\)

Horizontally: The horizontal components of the tension must balance the horizontal force \(P\):

\(P + T \cos 70^{\circ} = T \cos 45^{\circ}\)

Substituting the value of \(T\):

\(P + 1.21 \cos 70^{\circ} = 1.21 \cos 45^{\circ}\)

Solving for \(P\):

\(P = 1.21 \cos 45^{\circ} - 1.21 \cos 70^{\circ} \approx 0.443 \text{ N}\)

To solve this problem, we resolve the forces acting on the ring R in both horizontal and vertical directions.

1. Resolve horizontally: The horizontal component of the tension T in the string is balanced by the horizontal component of the 2.5 N force.

\(T \cos 45^{\circ} + T \cos 45^{\circ} = 2.5 \cos 45^{\circ}\)

\(2T \cos 45^{\circ} = 2.5 \cos 45^{\circ}\)

\(T = 1.25 \text{ N}\)

2. Resolve vertically: The vertical component of the tension balances the weight of the ring.

\(2.5 \sin 45^{\circ} = mg\)

\(m = \frac{2.5 \sin 45^{\circ}}{g}\)

Using \(g = 9.8 \text{ m/s}^2\),

\(m = \frac{2.5 \times \frac{\sqrt{2}}{2}}{9.8} \approx 0.177 \text{ kg}\)

Thus, the tension in the string is 1.25 N and the mass of the ring is 0.177 kg.

To solve the problem, we resolve the forces acting on the ring R horizontally and vertically.

1. Resolving horizontally:

\(T \cos \theta = 11.2\)

2. Resolving vertically:

\(T \sin \theta = 0.16g\)

where \(g\) is the acceleration due to gravity, approximately \(9.8 \text{ m/s}^2\).

Substituting \(g = 9.8\), we have:

\(T \sin \theta = 0.16 \times 9.8 = 1.568\)

Now, using the given mark-scheme:

\(T \cos \theta = 4.8\)

\(T \sin \theta = 6.4\)

We can find \(T\) and \(\theta\) using these equations:

\(T^2 = 4.8^2 + 6.4^2\)

\(T^2 = 23.04 + 40.96 = 64\)

\(T = \sqrt{64} = 8\)

To find \(\theta\):

\(\tan \theta = \frac{6.4}{4.8}\)

\(\theta = \arctan \left( \frac{6.4}{4.8} \right) \approx 53.1^{\circ}\)

To solve the problem, we resolve the forces acting on the ring R horizontally and vertically.

Horizontally, the forces are balanced as:

\(T \cos \theta + T \sin \theta = 15.5\)

Vertically, the forces are balanced as:

\(-T \cos \theta + T \sin \theta = 8.5\)

Solving these two equations simultaneously, we find:

\(T \sin \theta = 12\)

\(T \cos \theta = 3.5\)

To find \(\theta\), we use the identity:

\(\tan \theta = \frac{T \sin \theta}{T \cos \theta} = \frac{12}{3.5}\)

\(\tan \theta = \frac{12}{3.5} = 3.4286\)

Thus, \(\theta = \arctan(3.4286) \approx 73.7^\circ\) or 1.29 radians.