Question

a boy falls freely from a building of height 320m. After 5s Superman jumps downward with initial speed u. Such that the boy can be saved, the minimum value of u is​

Answer 1

Answer:

Explanation:

Ok I have done

Answer 2

The minimum value of initial speed (u0) of the Superman is 91.667m/s.

Given:-

Height of the building (h) = 320m

Time after which Superman jumps (t') = 5s

To Find:-

The minimum value of initial speed (u0) of the Superman.

Solution:-

We can easily find the minimum value of initial speed (u) of the Superman by using these simple steps.

As,

Height of the building (h) = 320m

Time after which Superman jumps (t0) = 5s

Initial speed of boy (u) = 0

So, According to the formula,

For boy, time taken to come down,

$h = ut + \frac{1}{2} a {t}^{2}$

$320 = 0 \times t + \frac{1}{2} \times 10 \times {t}^{2}$

$320 = 5 \times {t}^{2}$

${t}^{2} = 64$

$t = \sqrt{64}$

t = 8sec

So, we can say the boy will take 8 sec to fall.

And the Superman jumps after 5 sec, so Superman has to cover the same distance in less time i.e. 3ec.

Again,

$h = uot + \frac{1}{2} a{to}^{2}$

$320 = uo \times 3 + \frac{1}{2} \times 10 \times {3}^{2}$

$320 = 3uo + 5 \times 9$

$3uo \: = 320 - 45$

$3uo = 275$

$uo = \frac{275}{3}$

u0 = 91.667m/s

Hence, minimum value of initial speed (u0) of the Superman is 91.667m/s.

#SPJ2