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How wheel + Tyre diameter affects a vehicle’s speed

I have been told a larger wheel/tyre decrease acceleration because its harder to turn the wheel making the car rev slower.

But the same person tells me it will increase the top speed.

My question is if the car has a max rev of 8000rpm but only reaches 7000rpm in its highest gear would a smaller wheel/tyre not make it easier for the car to rev higher thus possible increasing the top speed by using a smaller wheel?

(Garry asked)

Answer:
As wheel radius increases, its top speed increases for a given RPM since for a given RPM the speed of the vehicle is directly proportional to its radius.
The distance traveled in one rotation = 2 π R
But now, there is another effect also here. As the radius of tyre increases, its moment of inertia increases and it would be harder for the engine to rotate it. So, the engine will not be able to turn it with the same ease as before, but however, there will be an increase in top speed other conditions remaining the same.
Monster Truck
Refer to http://wahiduddin.net/calc/calc_speed_rpm.htm for a calculation of top speed vs tyre radius

The problem of a rock thrown vertically up

A rock is thrown vertically upward from the ground with an initial speed 15m/s.

a. how high does it go
b. how much time is required for the rock to reach its maximum height?
c. what is the rock’s height at t=2.00s?

(Posted by Merhawi)

Answer:

(a)

u=15m/s

a=-10m/s2

v=0 m/s (at the max height)

S=?

v2-u2=2aS

S=v2-u2/2a

=225/20

=11.25 m

(b) From the above case

using v=u+at

t=v-u/a=1.5s

(c) Use S = ut + 1/2 at2

put t=2s, u = 15m/s, a=-10m/s2

S=30 – 20 = 10 m

(If you use g = 9.8 m/s2 The answers will be slightly different)

Relative velocity in free fall

If a person jumps out of a plane, and a few seconds later, another person jumps, why is it that the difference in their velocities stays the same? Shouldn’t it decrease because eventually, the first diver will reach maximum velocity, but the other diver will be slower at first, but then he reaches max. velocity as well…I’m not wording it the best way, but any help would be greatly appreciated :]

[Posted by Iris]

Both are examples for free fall. The velocity at any instant is given by v = gt

If for the first one, time = t and for the second who jumps after n seconds, time=t-n

Therefore, velocity of the first one at any instant, v1=gt

for second one, v2=g(t-n)

The difference in velocities,

v1-v2 = gn, which shows that the difference in velocity remains constant.

This is because, both are moving with the same acceleration and their velocities are increasing at the same rate

i want score max marks in physics. So how much time must be given to study it ?

Amandeep asked:

“i want to score max marks in Physics. So how much time to be given to study it”

Mathew Abraham responds:

First of all I would like to say that “Don’t study just for marks!! “.

You have to concentrate on concepts and ideas and don’t leave until you fully grasped the idea. If you have understood the basic concept and how to apply it in different situations, learning Physics is just fun.

The time you should spend for studying Physics depends on how easy you can grasp the ideas.

Having a master plan is very important.

Depending on the time available to you before exams, arrange a daily plan of revision and ensure that you reach the target.

Have a regular plan for solving numerical problems systematically. Clarifying your doubts and questions related to the topic is important. (AskPhysics is always ready to give you an answer)

If you are a candidate for the AISSCE 2011, Then the following strategy will help you.

  • Have a collection of all 3 marks and 5 marks questions and their answers prepared in the most presentable manner. (show it to your teacher for any corrections or modifications) You can consult some text books for preparing the first draft. The 3 and 5 marks alone constitute 60 % of the total marks.
  • Solve and practice all the exercises from NCERT text (including examples and exercises) Many publishers have released solutions for NCERT exercises. If you can get one, it will be helpful.
  • As a last step practice at least 5 Previous Board Papers. (The more the best)
  • If you do the above, you can easily score more than 90% marks or more.
  • If any of the questions could not be answered by you, please feel free to ask here at www.askphysics.com

Once again I would like to remain, It’s not time; but the task in hand is more important.

Wish you all the best.

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Schrodinger’s Cat in Daily Life

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