12.A bullet of mass 20 g has an initial speed of 1 ms,
just before it starts penetrating a mud wall of thickness 20
cm. If the wall offers a mean resistance of 2.5 * 10-N,
the speed of the bullet after emerging from the other side
of the wall is close to :
(a) 0.3 ms? (b) 0.1 ms-' (c) 0.7 ms? (d) 0.4 ms -1
Answers
Answer:
Option (c) 0.7 m/s
Explanation:
Mass of the bullet = 20 g
Initial speed of the bullet = 1 m/s
The bullet hits the wall with speed 1 m/s
After that a resisting force of 2.5 × 10⁻² N acts on the bullet
Acceleration due to this force = F/m = (2.5 × 10⁻²)/(20 × 10⁻³)
= 25/20
= 5/4 m/s²
Thickness of wall = 20 cm = 0.2 m
The bullet travels 0.2 m with a retardation of 5/4 m/s² acting on it
Using the third equation of motion
v² = u² - 2as
v² = 1² - 2 × (5/4) × 0.2
⇒ v² = 1 - 5 × 0.1
⇒ v² = 1 - 1/2 = 1/2
⇒ v = 1/√2 = √2/2 = 1.414/2 = 0.7 m/s
Therefore, the correct option is option (c)
Answer:
0.7 m/s
Explanation-
Mass of the bullet = 20 g
Initial speed of the bullet = 1 m/s
The bullet hits the wall with speed 1 m/s
After that a resisting force of 2.5 × 10⁻² N acts on the bullet
Acceleration due to this force = F/m = (2.5 × 10⁻²)/(20 × 10⁻³)
= 25/20
= 5/4 m/s²
Thickness of wall = 20 cm = 0.2 m
The bullet travels 0.2 m with a retardation of 5/4 m/s² acting on it
Using the third equation of motion
v² = u² - 2as
v² = 1² - 2 × (5/4) × 0.2
⇒ v² = 1 - 5 × 0.1
⇒ v² = 1 - 1/2 = 1/2
⇒ v = 1/√2 = √2/2 = 1.414/2 = 0.7 m/s
Therefore, the correct option is option (c)