Comic-strip hero Superman meets an asteroid in outer space and hurls it at 800 m/s, as fast as a bullet. The asteroid is a thousand times more massive than Superman. In the strip, Superman is seen at rest after the throw. Taking physics into account, what would be his recoil speed (in km/s)?

800km/s

Explanation:

Initial momentum = final momentum

the total momentum is zero, Before the release of the asteroid , but Superman and the asteroid are not moving.

So, according to the Conservation of momentum the total momentum when the astronaut is been thrown will equals to zero . Then we can say

Initial momentum = final momentum

Because the momentum of the Superman immediately the asteroid is been thrown is equal to the momentum of the asteroid

Momentum =(mass ×velocity)

the mass of the asteroid i= 1000M

Given velocity = 800 m/s,

momentum =(1000M)(800 m/s)

= 800,000M m/s.

to get the answer, we need to divide by Superman's mass, M, which gives his recoil velocity of 800,000 m/s.

But we're told to convert to km/ s

We know that 1m/s=0.001km/s

=(800,000M m/s)× (0.001km/s)

=800km/s

Therefore, his recoil speed (in km/s) is 800km/s

the minimum constant speed at which she can catch the train is 2.7 m/s

given:

acceleration = 0.6

time = 4.5 s

to find:

velocity = ?

formula used:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

solution:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

v = 0 + (0.6 × 4.5)

v = 2.7 m/s

the minimum constant speed at which she can catch the train is 2.7 m/s