5. Work, energy and power
A section of Physics, 9702
Listing 10 of 242 questions
Define power. State what is meant by gravitational potential energy. An aircraft of mass 1200 kg climbs upwards with a constant velocity of 45 m s–1, as shown in . velocity 45 m s–1 thrust force 2.0 × 103 N aircraft mass 1200 kg path of aircraft (not to scale) The aircraft’s engine produces a thrust force of 2.0 × 103 N to move the aircraft through the air. The rate of increase in height of the aircraft is 3.3 m s–1. Calculate the power produced by the thrust force. power = W Determine, for a time interval of 3.0 minutes, 1. the work done by the thrust force to move the aircraft, work done = J 2. the increase in gravitational potential energy of the aircraft, increase in gravitational potential energy = J 3. the work done against air resistance. work done = J Use your answer in part 3 to calculate the force due to air resistance acting on the aircraft. force = N With reference to the motion of the aircraft, state and explain whether the aircraft is in equilibrium.
9702_w18_qp_21
THEORY
2018
Paper 2, Variant 1
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State what is meant by kinetic energy. A cannon fires a shell vertically upwards. The shell leaves the cannon with a speed of 80 m s–1 and a kinetic energy of 480 J. The shell then rises to a maximum height of 210 m. The effect of air resistance is significant. Show that the mass of the shell is 0.15 kg. For the movement of the shell from the cannon to its maximum height, calculate 1. the gain in gravitational potential energy, gain in gravitational potential energy = J 2. the work done against air resistance. work done = J Determine the average force due to the air resistance acting on the shell as it moves from the cannon to its maximum height. force = N The shell leaves the cannon at time t = 0 and reaches maximum height at time t = T. On , sketch the variation with time t of the velocity v of the shell from time t = 0 to time t = T. Numerical values of v and t are not required. v t T The force due to the air resistance is a vector quantity. Compare the force due to the air resistance acting on the shell as it rises with the force due to the air resistance as it falls.
9702_w18_qp_23
THEORY
2018
Paper 2, Variant 3
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A spring is fixed at one end and is compressed by applying a force to the other end. The variation of the force F acting on the spring with its compression x is shown in . x / m F F1 0.045 A compression of 0.045 m is produced when a force F1 acts on the spring. The spring has a spring constant of 800 N m−1. Determine F1. F1 = N Use to show that, for a compression of 0.045 m, the elastic potential energy of the spring is 0.81 J. A child’s toy uses the spring in to launch a ball of mass 0.020 kg vertically into the air. The ball is initially held against one end of the spring which has a compression of 0.045 m. The spring is then released to launch the ball. The kinetic energy of the ball as it leaves the toy is 0.72 J. The toy converts the elastic potential energy of the spring into the kinetic energy of the ball. Use the information in to calculate the percentage efficiency of this conversion. efficiency = % Determine the initial momentum of the ball as it leaves the toy. momentum = N s The ball in leaves the toy at point A and moves vertically upwards through the air. Point B is the position of the ball when it is at maximum height h above point A, as illustrated in . h A B ball reaches maximum height at point B ball at point A kinetic energy 0.72 J mass 0.020 kg (not to scale) The gravitational potential energy of the ball increases by 0.60 J as it moves from A to B. Calculate h. h = m Determine the average force due to air resistance acting on the ball for its movement from A to B. average force = N When there is air resistance, the ball takes time T to move from A to B. State and explain whether the time taken for the ball to move from A to its maximum height will be more than, less than or equal to time T if there is no air resistance.
9702_w20_qp_22
THEORY
2020
Paper 2, Variant 2
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Define power. A car of mass 1700 kg moves in a straight line along a slope that is at an angle θ to the horizontal, as shown in . horizontal car, mass 1700 kg slope A B 25 m θ (not to scale) The car moves at constant velocity for a distance of 25 m from point A to point B. Air resistance and friction provide a total resistive force of 440 N that opposes the motion of the car. For the movement of the car from A to B: state the change in the kinetic energy change in kinetic energy = J calculate the work done against the total resistive force. work done = J The movement of the car in from A to B causes its gravitational potential energy to increase by 4.8 × 104 J. Calculate: the increase in vertical height h of the car for its movement from A to B h = m angle θ. θ = ° The engine of the car in produces an output power of 1.7 × 104 W to move the car along the slope. Calculate the time taken for the car to move from A to B. time = s
9702_w21_qp_22
THEORY
2021
Paper 2, Variant 2
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Questions Discovered
242