5.1. Energy conservation
A subsection of Physics, 9702, through 5. Work, energy and power
Listing 10 of 149 questions
A motor uses a wire to raise a block, as illustrated in . motor wire block, weight 1.4 × 104 N Z Y X (not to scale) The base of the block takes a time of 0.49 s to move vertically upwards from level X to level Y at a constant speed of 0.64 m s–1. During this time the wire has a strain of 0.0012. The wire is made of metal of Young modulus 2.2 × 1011 Pa and has a uniform cross-section. The block has a weight of 1.4 × 104 N. Assume that the weight of the wire is negligible. Calculate: the cross-sectional area A of the wire A = m2 the increase in the gravitational potential energy of the block for the movement of its base from X to Y. increase in gravitational potential energy = J The motor has an efficiency of 56%. Calculate the input power to the motor as the base of the block moves from X to Y. input power = W The base of the block now has a uniform deceleration of magnitude 1.3 m s–2 from level Y until the base of the block stops at level Z. Calculate the tension T in the wire as the base of the block moves from Y to Z. T = N The base of the block is at levels X, Y and Z at times tX, tY and tZ respectively. On , sketch a graph to show the variation with time t of the distance d of the base of the block from level X. Numerical values of d and t are not required. d tX tY t tZ
9702_m23_qp_22
THEORY
2023
Paper 2, Variant 2
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An object is suspended from a vertical spring as shown in . spring object oscillation The object is displaced vertically and then released so that it oscillates, undergoing simple harmonic motion. shows the variation with displacement x of the energy E of the oscillations. –1.6 –1.2 –0.8 –0.4 0.4 0.8 1.2 1.6 1.0 2.0 3.0 4.0 5.0 6.0 7.0 x / cm E / mJ P Q R The kinetic energy, the potential energy and the total energy of the oscillations are each represented by one of the lines P, Q and R. State the energy that is represented by each of the lines P, Q and R. P Q R The object has a mass of 130 g. Determine the period of the oscillations. period = s State the cause of damping. A light card is attached to the object. The object is displaced with the same initial amplitude and then released. During each complete oscillation the total energy of the system decreases by 8.0% of the total energy at the start of that oscillation. Determine the decrease in total energy, in mJ, of the system by the end of the first 6 complete oscillations. energy lost = mJ State, with a reason, the type of damping that the card introduces into the system.
9702_m23_qp_42
THEORY
2023
Paper 4, Variant 2
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Use A car battery has an internal resistance of 0.060 Ω. It is re-charged using a battery charger having an e.m.f. of 14 V and an internal resistance of 0.10 Ω, as shown in . battery charger car battery 0.060 Ω E 0.10 Ω 14 V + – At the beginning of the re-charging process, the current in the circuit is 42 A and the e.m.f. of the battery is E (measured in volts). For the circuit of , state 1. the magnitude of the total resistance, resistance = Ω 2. the total e.m.f. in the circuit. Give your answer in terms of E. e.m.f. = V Use your answers to and data from the question to determine the e.m.f. of the car battery at the beginning of the re-charging process. e.m.f. = V Examiner’s Use For the majority of the charging time of the car battery, the e.m.f. of the car battery is 12 V and the charging current is 12.5 A. The battery is charged at this current for 4.0 hours. Calculate, for this charging time, the charge that passes through the battery, charge = C the energy supplied from the battery charger, energy = J the total energy dissipated in the internal resistance of the battery charger and the car battery. energy = J Use your answers in to calculate the percentage efficiency of transfer of energy from the battery charger to stored energy in the car battery. efficiency = %
9702_s07_qp_2
THEORY
2007
Paper 2, Variant 0
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Questions Discovered
149