Question

An open knife edge of mass 200 g is dropped
from height 5m on a cardboard. If the knife
edge penetrates distance 2m into the card
board, the average resistance offered by the
cardboard to the knife edge is (g = 10 m/s2)
1) 7N 2) 25 N ' 3)35 N 4) None​

Answer 1

Explanation:

Given An open knife edge of mass 200 g is dropped from height 5 m on a cardboard. If the knife edge penetrates distance 2 m into the card board, the average  resistance offered by the  cardboard to the knife edge is (g = 10 m/s^2)

• Given mass m = 200 g
• Also height h = 5 m
• Now the knife edge penetrates into the cardboard at a distance of 2 m and so the height will be 2 m.
• So there will be retardation and due to this we need to find the average resistance offered.
• So initial velocity u = 0
• So potential energy is converted to kinetic energy.
•         So P.E = K.E
•      So mgh = 1/2 x m x v^2
•        So 10 x 5 = 1/2 v^2
•           Or v^2 = 2 x 10 x 5
•            Or v^2 = 100
•           Or v = 10 m /s^2 This is the final velocity.
•                        Now  after the knife penetrates cardboard  
•                           We have u = 10 m/s and v = 0
• Now we can take the equation of motion as
•                                So v^2 = u^2 + 2as
•                            Or 2as = v^2 – u^2
•                             2 x a x 2 = 0 – (10)^2
•                                  4a = - 100
•                            Or a = - 100 / 4
•                             Or a = - 25 m / s^2 (so retardation)
•                 Now Resistance Force = mass x retardation
•                                                     = 0.2 (200 g.) x 25
•                                                    = 5 kg-m / s^2
•                                                   = 5 N
• So Force will be 5 N
• Therefore the resistance offered by the cardboard is 5 N

Reference link will be

https://brainly.in/question/5068020

Answer 2

Answer:

7 N

Explanation:

the answer is7 Newton

you can solve this sum based on the given clues

u=√2 gh, using v^2-u^2=2 as retardation due to air resistance=a`=g+a

force due to air resistance=ma`