Question

A shot travelling at the speed of 200 ms is just able to pierce a
plank 5 cm thick. The velocity required to pierce a small plank
20cm thick is
1) 100ms-1
2) 300m& B) 400ms 4) 800ms​

Answer 1

Answer:

Explanation:

so initial velocity of the shot, u=200m/s

distance travelled before coming to rest,S= 5cm= 0.05m

final velocity, v=0

let the retardation be 'a'

we know,

v^2=u^2-2aS

or, 0= 40000-2a*0.05

or,a=40000/(2*0.05)

or, a= 4*10^5 m/sec^2

let the initial velocity required to pierce 20cm i.e 0.2m before coming to rest be 'u'm/sec

final velocity, v=0 m/sec

applying, v^2=u^2-2aS

0=u^2-2*4*10^5*0.2

or, u^2= 16*10^4

or, u= sqrt(16*10^4)

or, u=400 m/sec

the required velocity= 400m/sec