A bullet is fired through a board, 14.0 cm thick, with its line of motion perpen

Question

A bullet is fired through a board, 14.0 cm thick, with its line of motion perpendicular to the face of the board. If it enters with a speed of 450 m/s and emerges with a speed of 220 m/s, what is the bullet's acceleration as it passes through the board? A toy rocket, launched from the ground, rises vertically with an acceleration of 20 m/s^2 for 6.0 s until its motor stops. Disregarding any air resistance, what maximum height above the ground will the rocket achieve? a. 1.1 km b. 0.73km c. 1.9 km d. 0.39km e. 1.5 km

Explanation / Answer

3 )

given

u = 450 m/sec

v = 220 m/sec

s = 14 m

= 0.14 m

using equation

v2 - u2 = 2 a s

2202 - 4502 = 2 X a X 0.14

a = - 550357.1429 m/sec2

4 )

given

a = 20 m/sec2 ,

t = 6 sec

using s = 1/2 a t2

s = 360 m

using v = u + a t

we get v = 0 + 20 X 6

v = 120 m/sec

v2 = u2 + 2 a s

0 = 14400 - 2 X 9.8 X s

s = 14400 / 19.6

s = 734.69 m

tota height = 734.69 + 360

= 1094.69 m

~ = 1095 m

= 1.1 km ( rounded off value)

option " a " is correct

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