Oswald Blackwood [1888-1953], the inventor of the inventor of the Blackwood Ball

Question

Oswald Blackwood [1888-1953], the inventor of the inventor of the Blackwood Ballistic pendulum used in this lab, was a professor at the university of Pittsburgh and one of the founding members of the American Association of Physics Teachers Suppose the ball bearing (0.10 kg) in this experiment is shot with on initial velocity of 16.5 m/s. What is the initial momentum of the ball bearing? If the ball lodges in a ballistic pendulum that initially has a mass of 1.5 kg, find the velocity of the boll and cylinder just after the collision. What is the kinetic energy of the ball and cylinder following the collision? How high will the ball and cylinder swing?

Explanation / Answer

m1 =0.1 kg , u1 =16.5 m/s

(a) p = m1u1 = 0.1*16.5 = 1.65 kg.m/s

(b) m2 =1.5 kg

From conservation of momentum

m1u1 +0 = (m1+m2)v

v = 1.65/(0.1+1.5) =1.03 m/s

(c) K = (1/2)(m1+m2)v^2

K = 0.5*(0.1+1.5)(1.03*1.03)

K =0.85 J

(d) From conservation of energy

mgh = (1/2)mv^2

h = v^2/2g = (1.03*1.03)/(2*9.8)

h = 0.054 m

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