Rocket thrust to overcome weight – Rankers Physics

Uncategorized: Practice Problem & Solution

A 600 kg rocket is set for a vertical firing. If the exhaust speed is \(1000 \text{ ms}^{-1}\,) the mass of the gas ejected per second to supply the thrust needed to overcome the weight of rocket is: (1990)
\(117.6 \text{ kgs}^{-1}\)
\(58.6 \text{ kgs}^{-1}\)
\(6 \text{ kgs}^{-1}\)
\(76.4 \text{ kgs}^{-1}\)

Short Solution (Best for NEET):

To solve this problem, we apply the core principles of Uncategorized. Understanding the underlying formula is key to arriving at the correct answer below:

The thrust of a rocket is given by \(T = v_e \frac{dm}{dt}\,) where \(v_e\) is the exhaust speed and \(frac{dm}{dt}\) is the mass ejection rate. To overcome the rocket's weight \(Mg\), the thrust must equal the weight. So, \(v_e \frac{dm}{dt} = Mg\). Given \(M = 600 \text{ kg}\,) \(v_e = 1000 \text{ m/s}\,) and assuming \(g \approx 10 \text{ m/s}^2\), we have \(1000 \frac{dm}{dt} = 600 \times 10\). Thus, \(frac{dm}{dt} = 6 \text{ kg/s}\).

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