A ball is projected vertically upwards. Which of the following best describes the energy transfer which occurs as it travels upwards?Energy from its thermal store is transferred to its gravitational potential storeEnergy from its gravitational potential store is transferred to its kinetic storeEnergy from its kinetic store is transferred to its gravitational potential storeEnergy from its elastic potential store is transferred to its gravitational potential store2A skateboarder initially has 5 kJ of kinetic energy. As she freewheels along a flat section of path, she does 400 J of work against friction and air resistance. Calculate her final kinetic energy.405 J5200 J4.6 kJ395 J3Calculate the kinetic energy of a truck of mass 10,000 kg which is travelling at 20 m/s.2 MJ200,000 J100 kJ4,000,000 J4A 300 kg boulder is resting at the top of a 50 m-high hill. Calculate its gravitational potential energy. Take g = 10 N/kg.15,000 J360 J150,000 J1,500 J5A tennis ball of mass 100 grams is dropped from a height of 2 metres. Calculate its speed just before it hits the ground. In answering this question, you may assume that all of the gravitational potential energy which is initially stored by the ball is transferred to its kinetic store as it falls through the air. Take g = 10 N/kg.3.16 m/s2 m/s6.32 m/s20 m/s
Question
A ball is projected vertically upwards. Which of the following best describes the energy transfer which occurs as it travels upwards?Energy from its thermal store is transferred to its gravitational potential storeEnergy from its gravitational potential store is transferred to its kinetic storeEnergy from its kinetic store is transferred to its gravitational potential storeEnergy from its elastic potential store is transferred to its gravitational potential store2A skateboarder initially has 5 kJ of kinetic energy. As she freewheels along a flat section of path, she does 400 J of work against friction and air resistance. Calculate her final kinetic energy.405 J5200 J4.6 kJ395 J3Calculate the kinetic energy of a truck of mass 10,000 kg which is travelling at 20 m/s.2 MJ200,000 J100 kJ4,000,000 J4A 300 kg boulder is resting at the top of a 50 m-high hill. Calculate its gravitational potential energy. Take g = 10 N/kg.15,000 J360 J150,000 J1,500 J5A tennis ball of mass 100 grams is dropped from a height of 2 metres. Calculate its speed just before it hits the ground. In answering this question, you may assume that all of the gravitational potential energy which is initially stored by the ball is transferred to its kinetic store as it falls through the air. Take g = 10 N/kg.3.16 m/s2 m/s6.32 m/s20 m/s
Solution
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The best description for the energy transfer that occurs as the ball travels upwards is "Energy from its kinetic store is transferred to its gravitational potential store". This is because as the ball is projected upwards, it slows down due to gravity, thus its kinetic energy (energy of motion) decreases while its gravitational potential energy (energy due to its position in a gravitational field) increases.
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The skateboarder initially has 5 kJ (or 5000 J) of kinetic energy. She does 400 J of work against friction and air resistance. This work done is energy transferred from her kinetic energy store. So, her final kinetic energy is the initial kinetic energy minus the work done. That is 5000 J - 400 J = 4600 J or 4.6 kJ.
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The kinetic energy of an object can be calculated using the formula KE = 1/2 mv^2, where m is the mass and v is the velocity. Substituting the given values, we get KE = 1/2 * 10000 kg * (20 m/s)^2 = 2,000,000 J or 2 MJ.
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The gravitational potential energy of an object can be calculated using the formula GPE = mgh, where m is the mass, g is the gravitational field strength, and h is the height. Substituting the given values, we get GPE = 300 kg * 10 N/kg * 50 m = 150,000 J.
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The speed of the tennis ball just before it hits the ground can be calculated by equating the initial gravitational potential energy to the final kinetic energy (assuming no energy losses). This gives us 1/2 mv^2 = mgh, where m is the mass, v is the velocity, g is the gravitational field strength, and h is the height. Solving for v gives us v = sqrt(2gh). Substituting the given values, we get v = sqrt(2 * 10 N/kg * 2 m) = 6.32 m/s.
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