Jobs & Education1 min ago
lighter or the same
23 Answers
A lorry with a sealed load of birds is making a short journey, the driver encounters a steep hill ,when half way up realises he is not going to make it due to the weight of the birds, he has the bright idea of banging on the side of the lorry to make the birds fly, thus thinking it will be lighter therefore getting up the hill?? yes or no
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If the lorry is sealed then the average weight is the same whether the birds fly or not.
He could perhaps succeed though. If he raps on the back of the cab the birds will take off, momentarily increasing the weight. Immediately afterwards the weight of the birds will reduce slightly to keep the average constant. Perhaps he can drive a metre up the hill in this time before waiting for the birds to settle and repeat the process.
I'd release them and try to catch a few at the top of the hill.
He could perhaps succeed though. If he raps on the back of the cab the birds will take off, momentarily increasing the weight. Immediately afterwards the weight of the birds will reduce slightly to keep the average constant. Perhaps he can drive a metre up the hill in this time before waiting for the birds to settle and repeat the process.
I'd release them and try to catch a few at the top of the hill.
What he should do is nip into a shop (or several shops if the owner of the first one has decided that diversification in this current economic climate is not a good model) and get a long bit string, scissors, a bag, a pin, bird food, several balloons and helium.
He puts the bird food into the bag and ties the bag to the inflated balloons. He cuts the string into shorter lengths and ties one end to the front bumper and the other end to one of the birds he has removed from the lorry. He repeats this for each bird.
He then ties the balloons to the bumper and pricks the bag of bird food so that a wee bit can trickle out. He releases the balloon and the birds' attention is drawn to the bag.
He starts his engine which startles the birds and they fly toward the trickling bird food. As the string tightens, they are then adding pulling power to the lighter lorry and it manages to get up the steep hill.
Simple!
He puts the bird food into the bag and ties the bag to the inflated balloons. He cuts the string into shorter lengths and ties one end to the front bumper and the other end to one of the birds he has removed from the lorry. He repeats this for each bird.
He then ties the balloons to the bumper and pricks the bag of bird food so that a wee bit can trickle out. He releases the balloon and the birds' attention is drawn to the bag.
He starts his engine which startles the birds and they fly toward the trickling bird food. As the string tightens, they are then adding pulling power to the lighter lorry and it manages to get up the steep hill.
Simple!
Surely not, the parts of the pressure waves that are deflected to the side would not be supporting the bird upwards, but pushing it towards the opposite side, otherwise you would have a force being exerted on the side of the lorry with no equal opposite force. The force going downwards must at least match that needed to support the weight of the bird else it would fall out the sky
though what would happen if the floor of the lorry was a mesh? then the lorry would have to get lighter in my reckoning.
though what would happen if the floor of the lorry was a mesh? then the lorry would have to get lighter in my reckoning.
Good question ambassabuild and some great answers.
On a similar tack, if you stood at the front of a forward moving train carriage that was travelling at a constant speed of say, 100mph and jumped vertically for a period of 1 second, would you be closer to the rear of the train when you landed. And if so, how long would it take to travel the length of a 20' carriage presuming the train speed remained constant and the jump rate was one 1 second jump followed by a four second pause. Therefore 12 jumps per minute.
Sorry for jumping your post, a, but there are some sharp minds on ab this evening.
On a similar tack, if you stood at the front of a forward moving train carriage that was travelling at a constant speed of say, 100mph and jumped vertically for a period of 1 second, would you be closer to the rear of the train when you landed. And if so, how long would it take to travel the length of a 20' carriage presuming the train speed remained constant and the jump rate was one 1 second jump followed by a four second pause. Therefore 12 jumps per minute.
Sorry for jumping your post, a, but there are some sharp minds on ab this evening.
GEEMAC, Jumping up and down on a moving train employs totally different physics than the sealed lorry with birds.
When jumping in a moving train you do land slightly behind where you left the ground. The moment you feet leave the floor your body starts to slow down so you must land behind where you started to jump, even if ever so slightly. The distance traveled backward per jump depends on variables such as body weight, how high is the jump and how high above sea level the train is traveling.
When jumping in a moving train you do land slightly behind where you left the ground. The moment you feet leave the floor your body starts to slow down so you must land behind where you started to jump, even if ever so slightly. The distance traveled backward per jump depends on variables such as body weight, how high is the jump and how high above sea level the train is traveling.
Sure. It would take a lot of jumps though. With one 12" jump on a 60mph train by an average person we are talking millimetres. If someone has a window open the distance will be slightly more. If done on an open topped double decker (not to be recommended if approaching an overhead viaduct) we are talking inches due to even more wind resistance.
Jumping on a train depends on the location and direction of the train. It doesn�t depend on the speed of the train, certainly if the speed is less than 1000 kilometres per hour. You land in the same place on the train whether it is moving or not.
If you jump straight up you will land about 10 microns to the West of where you started.
So if the train is travelling West you will land nearer the front. If it is travelling East you'll land nearer the back. You'll land a bit towards the side if the train is going North or South.
This is because the Earth rotates West to East. When you jump vertically your angular velocity decreases in order to keep your angular momentum constant (as you are further from the centre of the Earth) so you will land slightly to the West.
This assumes a British train. The distance will be about double for a Sudanese train, and zero in Antarctica.
Also, you must stay inside the train so that we can neglect air movement, and you must be perfectly symmetrical � so don�t puff out your breath to propel yourself backwards.
Back to the truck of birds.
If the truck is sealed then there are only two ways that the birds can affect the truck. They can perform repeated movements where one move helps the driver and the next move hinders him. Examples are: all flying to the front while the driver keeps his brakes on, then all flying to the back while the driver accelerates up the hill; or all repeatedly taking off and landing together as suggested in a previous post.
The second method is even more far-fetched. The birds need to link wings and swarm very quickly around a central pole to form a gyroscope. The rotation of the Earth will then generate a miniscule force on the truck. If the direction is correct, and if the truck is very, very close to being able to climb the hill, the extra force could in theory, but not in practice, be sufficient.
If you jump straight up you will land about 10 microns to the West of where you started.
So if the train is travelling West you will land nearer the front. If it is travelling East you'll land nearer the back. You'll land a bit towards the side if the train is going North or South.
This is because the Earth rotates West to East. When you jump vertically your angular velocity decreases in order to keep your angular momentum constant (as you are further from the centre of the Earth) so you will land slightly to the West.
This assumes a British train. The distance will be about double for a Sudanese train, and zero in Antarctica.
Also, you must stay inside the train so that we can neglect air movement, and you must be perfectly symmetrical � so don�t puff out your breath to propel yourself backwards.
Back to the truck of birds.
If the truck is sealed then there are only two ways that the birds can affect the truck. They can perform repeated movements where one move helps the driver and the next move hinders him. Examples are: all flying to the front while the driver keeps his brakes on, then all flying to the back while the driver accelerates up the hill; or all repeatedly taking off and landing together as suggested in a previous post.
The second method is even more far-fetched. The birds need to link wings and swarm very quickly around a central pole to form a gyroscope. The rotation of the Earth will then generate a miniscule force on the truck. If the direction is correct, and if the truck is very, very close to being able to climb the hill, the extra force could in theory, but not in practice, be sufficient.
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