Question

A car of mass 900 kg is travelling at a steady speed of 30 m/s against a resistive force of 2000 N, as illustrated in figure.

(i) Calculate the kinetic energy of the car. (ii) Calculate the energy used in 1.0 s against the resistive force. (iii) What is the minimum power that the car engine has to deliver to the wheels? (iv) What form of energy is in the fuel, used by the engine to drive the car?

  • Work and energy CBSE Class 9
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Answer

(๐ข) Kinetic energy = {1\over2}๐‘š๐‘ฃ2

={1\over2}ร— 900 ร— (30)2

= {1\over2}ร— 900 ร— 900

= 4,05,000 J

(๐ข๐ข) Energy used = Work done against resistive force

= Force ร— Distance

= 2,000 ร— 30 = 60,000 J = 60 kJ

(iii) Minimum power = {Energy\ used \over Time\ taken}

= {60,000 J \over 1s} = 60,000 W = 60 kW

(iv) Chemical energy.

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