CIE iGCSE Co-Ordinated Science P1.5.2 Turning effect of forces Exam Style Questions Paper 4
Question
Fig. 3.1 shows a crane lifting a wooden crate.
(a) The crane is in equilibrium.
(i) The 1200 N counterweight is 5.0 m away from the pivot.
Calculate the moment of the counterweight about the pivot.
▶️Answer/Explanation
Answer: 6000 Nm
Explanation: The moment (M) is calculated using the formula \( M = F \times d \), where \( F \) is the force and \( d \) is the distance from the pivot. Here, \( F = 1200 \, \text{N} \) and \( d = 5.0 \, \text{m} \). Therefore, \( M = 1200 \times 5.0 = 6000 \, \text{Nm} \).
(ii) Determine the moment of the crate about the pivot.
▶️Answer/Explanation
Answer: 6000 Nm
Explanation: Since the crane is in equilibrium, the moment of the crate about the pivot must be equal to the moment of the counterweight. Therefore, the moment of the crate is also 6000 Nm.
(b) The crate gains 105 kJ of gravitational potential energy as it is lifted through a height of 42 m.
Calculate the mass of the crate. The gravitational field strength, \( g \), is 10 N/kg.
▶️Answer/Explanation
Answer: 250 kg
Explanation: The gravitational potential energy (GPE) is given by the formula \( \text{GPE} = m \times g \times h \), where \( m \) is the mass, \( g \) is the gravitational field strength, and \( h \) is the height. Rearranging the formula to solve for mass, we get \( m = \frac{\text{GPE}}{g \times h} \). Substituting the given values, \( m = \frac{105000}{10 \times 42} = 250 \, \text{kg} \).
(c) The crane uses an electric motor. Fig. 3.2 shows a simple d.c. motor.
(i) State the name of the component labelled Q in Fig. 3.2.
▶️Answer/Explanation
Answer: Split-ring commutator
Explanation: The component labelled Q is the split-ring commutator, which reverses the direction of current in the coil every half rotation, ensuring continuous rotation of the motor.
(ii) Draw an arrow on Fig. 3.2 to show the direction of the magnetic field.
▶️Answer/Explanation
Answer: Arrow drawn from N to S
Explanation: The magnetic field direction is from the North pole (N) to the South pole (S) of the magnet.
(iii) State two ways to increase the speed at which the coil rotates.
▶️Answer/Explanation
Answer:
- Increase the current
- Increase the magnetic field strength
Explanation: The speed of the coil rotation can be increased by increasing the current through the coil or by increasing the strength of the magnetic field. Both methods increase the force acting on the coil, resulting in faster rotation.