Answer:
Upward force on the boy will be 1024 N
Explanation:
We have given mass of the boy m = 80 kg
Acceleration due to gravity 
It is given that elevator is ascending with acceleration of 
So net acceleration on the boy = 9.8+3 = 12.8
( As the car elevator is moving ascending )
So upward force on the boy will be equal to F = m(g+a)
So 
So upward force on the boy will be 1024 N
The answer to this question is dropping it on a hard surface.
Answer:In first case
Explanation:
When two People pull the spring, let the applied force by each person be 
and spring constant of spring be k
so Total force is 
total extension according to Hooke's law is

When they detach the spring and apply force in opposite direction then force on either side is F so net extension is

so in first case there will be more extension
Answer:
solution
we know that .
s=ut+½at²
now, putting the values in the second equation of motion ,
we get,
S=20×10+1/2×(10)²
S=200+1×100
S=200+100
S=300m
the distance covered by given body or object in 10 seconds is 300 m.