Question

A car of mass 1000 kg is cruising at 120 km/hr. At this velocity the drag and friction forces that the engine needs to work against is equivalent to 450 N.


Q: Calculate the kinetic energy of the car when cruising at 120 km/hr.
Give your answer in Joules

Answer 1

Answer on Question #49062 – Engineering – Other

1. A car of mass $1000\,\mathrm{kg}$ is cruising at $120\,\mathrm{kmhr}$. At this velocity the drag and friction forces that the engine needs to work against is equivalent to $450\,\mathrm{N}$.

Q Calculate the kinetic energy of the car when cruising at $120\,\mathrm{kmhr}$.

Give your answer in Joules.

$$\begin{array}{l} m = 10^{3}\,\mathrm{kg} \\ v = 120\,\frac{\mathrm{km}}{\mathrm{hr}} = 33.3\,\frac{\mathrm{m}}{\mathrm{s}} \\ F = 450\,\mathrm{N} \\ \hline E - ? \end{array}$$

Solution.

The kinetic energy of an object, which has a mass $m$ and moves with the speed $v$ is

$$E = \frac{mv^2}{2}.$$

Let check the dimension: $[E] = kg \cdot \left(\frac{m}{s}\right)^2 = N \cdot m = J$.

Let evaluate the quantity: $E = \frac{10^{3} \cdot 33.3^{2}}{2} = 5.54 \cdot 10^{5}(J)$.

Answer: $5.54 \cdot 10^{5}$ Joules.

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