A bullet of mass 4g fired with a velocity of 50m/s enters a wall up to a depth 10cm. Calculate the resistance offered by the wall? Will the depth of penetration change if a bullet of mass 5g moving with a velocity of 40m/s strikes the wall?
CH -9 Class 9
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Answer:
The resistance offered will be expressed in terms of retardation or negative acceleration (m/s²)
To find the resistance we use the 3rd equation of motion
v2=u2+2asv2=u2+2as
vv = final velocity
uu = initial velocity
aa = acceleration (the unknown variable)
ss = displacement
After plugging in the values we get this linear equation
0=502+2(0.1)a0=502+2(0.1)a
vv is 0 as the bullet has stopped and displacement is 0.1 because 10 cm is converted to metres
Solving this equation
a=−12500m/s²a=−12500m/s²
Therefore the wall retards the bullet by 12500m/s²12500m/s² or the resistance offered by the wall is 12500m/s²12500m/s²
Note: the mass of the bullet wont affect the answer and is just given to throw you off track I suppose
As the unit of resistance isn't specified in the question the mass can be multiplied with the retardation to find the resistance in terms of Newtons
The answer comes out to be -50 Newtons therefore the resistance offered is 50 Newtons