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It takes 4200 Joules to heat up 1 kg of water by 1 C^o. If you have a kettle with a power of 2500 Watts, how long will it takes to boil 0.8 kg of water from an initial temperature of 25 C^o to the nearest second??

Energy required calculated using the equation for specific heat capacity: m c dT = dE where m is mass, c is specific heat capacity and dT is the change in temperature. Time taken is calculated using the rela...
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Answered by Benjamin C. • Physics tutor
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If a wire loop moves at constant speed into a region where there is a magnetic field, why is a current induced in the wire?

In this question, a square wire loop of length L and resistance R starts in a region with no magnetic field, and moves at a speed v into a region with magnetic field B, which is acting perpendicular to the a...
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Answered by Gus B. • Physics tutor
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From what height, h, should a rail-cart fall to complete a loop-the-loop of radius r without falling off a the track? Assume the track on which the rail-cart travels is smooth and express h in terms of r.

This question combines the principles of energy conservation and circular motion. The insight is to realise the condition for which the rail-cart will fall off of the track - when there is no contact force b...
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Answered by Benjamin R. • Physics tutor
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A box initially at rest is on a plank, of length 5m, that is elevated at an angle such that tan(a)=3/4. When it reaches the end of the plank it has velocity 5ms^-1. Calculate the average frictional force on the box.

In physics questions it is useful to not plug numbers in until the end and instead work through algebraically. Let's say the angle of elevation is a, the mass is m, the velocity at the end of the plank is v ...
Answered by • Physics tutor
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A ball of mass 500g is dropped from rest 2m above the ground. When it reaches the ground it is travelling at 5m/s. How much energy has been dissipated?

Initial energy (Gravitational Potential): E = mgh = 0.5 x 9.81 x 2 = 9.81J Final energy (Kinetic): E = mv 2 /2 = (0.5 x 5 2 )/2 = 6.25J Energy lost = 9.81 - 6.25 = 3.56J
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Answered by Georgina B. • Physics tutor
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