An automatic rifle fires 0.040-kg projectiles at a speed of 800 m/s.If the gunner holding the rifle in her hands can exert an average force of 160 N against the gun,the maximum number of projectiles she can fire in one minute is
A)15
B)300
C)800
D)4000
E)48,000

Question

Quizplus · Accepted Answer

The force exerted by the gunner on the rifle is given as F =160 N.
The work done by the gunner in firing one projectile is given by,

W = (1/2) mv^2 = (1/2) × 0.040 kg × (800 m/s)^2 = 12,800 J

The number of projectiles fired in one minute is given by,

N = (work done in one minute) / (work done per projectile)
N = (60 s) × (160 N) / (12,800 J) = 0.75

Therefore, the maximum number of projectiles that the gunner can fire in one minute is 0.75 or approximately 1 projectile per second. 
So, the maximum number of projectiles she can fire in one minute is 60 seconds × 1 projectile per second = 60 projectiles.
Since the possible answer closest to 60 is B (300), the answer is B.

An Automatic Rifle Fires 0