Question

A rifle with a weight of 30 N fires a 5.0-g bullet with a speed of 300 m/s. (a) Find

the recoil speed of the rifle. (b) If a 700-N man holds the rifle firmly against his
shoulder, find the recoil speed of man and rifle.

Answer 1

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Notes:

1grain = 64.8mg

1newton = 100g

= 300 m/s (speed)

= 30 × 100

= 3,000g (rifle mass)

= 5-g × 64.8

= 324mg (bullet mass)

= 700 × 100

= 70,000g (human mass)

= 70,000g + 3,000g

= 70,300g (human + rifle mass)

A) Newton's 2nd Law of Motion

M1 V1 = - m2 v2

Vr = - mb ÷ mr

Vb = - (324 ÷ 3,000) 300

= 32.4 m/s

B) Newton's 2nd Law of Motion

M1 V1 = - m2 v2

Vr = - mb ÷ mr

Vb = - (324 ÷ 70,300) 300

= 1.39 m/s

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