Question

A rocket of mass 5000 kg is to be projected vertically upward. The gases are exhausted vertically downwards with velocity 1000 ms⁻² with respect to the rocket. What is the minimum rate of burning the fuel so as to just lift the rocket upwards against gravitational attraction?(a) 49 kg s⁻¹ (b) 147 kg s⁻¹(c) 98 kg s⁻¹ (d) 196 kg s⁻¹

Answer 1

the answer is b.
I hope this answer is correct

Answer 2

Answer: a) 49kg/s

Explanation:

The rocket is projected in vertically upward direction.

Given data

Mass of rocket = 5000kg

g =9.8m/s^2

Where g is acceleration due to gravity.

Gases are exhausted in vertically downward direction.

Velocity = 1000m/s

The minimum force required is Fmin

Fmin = 5000*9.8

=49000 Newton

The minimum rate of burning the fuel so as to just lift the rocket is given by

dm/dt= fmin/v

=49000/1000

=49kg/s

Thus minimum rate of burning the fuel so as to just lift the rocket against gravitational field is 49kg/s.