Question

A commando jumps from the helicopter, after about 500 m his parachute opens and his velocity
reduces to 1/4 of the previous velocity. He covers next 1000 m with this speed before reaching the
ground. If the total time of flight is 30 sec, with what velocity had he started falling?
40 misec
50 m sec
150 misec​

Answer 1

Answer:

velocity he started falling =114.91m/s

Answer 2

Answer:

The correct answer for the original velocity of the commando falling is found to be 150 m/sec.

Step-by-step explanation:

We know that the expresssion for finding the time of an object is:

$time=\frac{distance}{speed}$

Let the velocity with which the commando started falling be $x$ m/sec.

Now, the time taken to cover the 500 meters without parachute will be:

$t_1=\frac{500}{x}$               ...(i)

Now, according to ques, when the parachute opens the velocity becomes: $\frac{x}{4}$ m/sec.

The time taken by commando to fall through 1000 meters will be:

$t_2=\frac{1000\times4}{x}$          ...(ii)

The total time of flight is given to us as: 30 sec

$t_1+t_2=30$

Substituting (i) and (ii), we get:

$\frac{500}{x}+\frac{4000}{x}=30$

$\frac{4500}{x}=30$

Using cross multiplication, we get:

$x=150$ m/sec

Thus, the original velocity was 150m/sec.