Question

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

A1. Calculate the kinetic energy of the car.

2. Calculate the energy used in 1.0 seconds against the resistive force.

3. What is the minimum power that the car engine has to deliver to the wheels?

Answer 1

a1=4,05,000j

a2=60kj

a3=60kw

Answer 2

(1) Kinetic energy, E = 405 kJ

(2) The energy used by the car is 60 kJ.

(3) Power is 60 kW

Explanation:

Mass of the car, m = 900 kg

Speed of the car is 30 m/s against a resistive force of 2000 N.

(1) The kinetic energy is due to the motion of the object. It is given by :

$K=\dfrac{1}{2}mv^2\\\\K=\dfrac{1}{2}\times 900\times (30)^2\\\\K=405000\ J\\\\K=405\ kJ$

(2) Let E is the energy used in 1.0 seconds against the resistive force. If the car is moving with a speed o 30 m/s. Then the distance covered by it in one second is 30 meters.

Work done or the energy used by the car is given by :

W = F × d

$W=2000\times 30\\\\W=60000\ J\\\\W=60\ kJ$

(3) Power that the car engine has to deliver to the wheels It is given by :

$P=\dfrac{W}{t}\\\\P=\dfrac{60\times 10^3\ J}{1\ s}\\\\P=60\times 10^3\ W\\\\P=60\ kW$

Learn more,

Kinematics

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