# An help needed

spirally
an urgent help needed

A bicycle pump which has a stroke of 20cm is used to force air into a tyre against a pressure
of 4bar.what length of stroke will be swept through before air begins to enter the tyre when the piston is pushed (a)slowly (b)quickly. Assume atmospheric pressure to be 1 bar

Staff Emeritus

spirally
pls help

i have practically no idea at all that is why i came to the forum for assistance.
how can i show what i have done when i have no ideas at all?

Homework Helper
Gold Member
Air (or any fluid) flows from high pressure to low pressure. When does the pressure in the bore of the pump just equal to the pressure in the tire?

unscientific

remember - every great scientist had humble beginings

InSpiRatioNy

i have practically no idea at all that is why i came to the forum for assistance.
how can i show what i have done when i have no ideas at all?

Sorry I can't help you, I can't remeber anything on this subject.

But a word of advice: If you don't know how to do it (no idea) say so, or you'll always get this reply.

StgIIIOvrDvn

A bicycle pump which has a stroke of 20cm is used to force air into a tyre against a pressure
of 4bar.what length of stroke will be swept through before air begins to enter the tyre when the piston is pushed (a)slowly (b)quickly. Assume atmospheric pressure to be 1 bar

In the case of gasses volume and pressure are inversely related. Meaning at 50% stroke ie. 10 cm the cylinder pressure will attain 2 bar, at 75% stroke it will be 4 bar, @ 15 cm. Rate has nothing to do with pressure, but will have an effect on the temerature of the compressed air, higher rate of compression means less time to cool off to ambient. Pressures vs stroke are assuming the temperature has returned to the same temp as the initial. Exact values for dynamic points must also include the energy input required to compress the air and are 0 Kelvin referenced. 4 Bar in your problem will in a real airpump be attained before the 15 cm mark due to compression heating of the air, but without cylinder area and ambient temp. of the uncompressed air heat transfer rates cannot be calculated.