On Land, Coal Is Transported Primarily by Train

Question

Examlex · Accepted Answer

The Answer is One tonne of coal has energy content of

3.1 imes 10 ^ { 10 } \mathrm {~J}

The total amount of coal on
the train is 120×110 tonnes = 13,200 tonnes. This has an energy content of

( 13,200 ext { tons } ) imes \left( 3.1 imes 10 ^ { 10 } \mathrm {~J} / ext { ton } ight) = 4.09 imes 10 ^ { 14 } \mathrm {~J} ext {. }

100 \mathrm {~km} / \mathrm { h }

corresponds to

( 100 \mathrm {~km} / \mathrm { h } ) imes ( 1000 \mathrm {~m} / \mathrm { km } ) / ( 3600 \mathrm {~s} / \mathrm { h } ) = 27.8 \mathrm {~m} / \mathrm { s }

A

1.5 - \mathrm { km }

long train will pass a reference point in

( 1500 \mathrm {~m} ) / ( 27.8 \mathrm {~m} / \mathrm { s } ) = 54 \mathrm {~s}

Thus the rate of flow of energy is

\frac { 4.09 imes 10 ^ { 14 } \mathrm {~J} } { 54 \mathrm {~s} } = 7.57 imes 10 ^ { 12 } \mathrm {~W} = 7.57 imes 10 ^ { 6 } \mathrm { MW }

Essay