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Question

A 7100 kg boxcar traveling 12.0 m/s strikes a second car. The two stick together and move off with a speed of 4.60 m/s.  What is the mass of the second car?  Express your answer using three significant figures.

Answer 1

Given

m1= 7100 kg

v_1i= 12.0 m/s

v_2i= 0 m/s

m_f= m₁+m₂

v_f= 4.60 m/s

We solve for v_2f and plug in the given values to determine the answer

p_1i+p_2i= p_f

⌋

m₁v_1i+m₂v_2i = m_fv_f

m₁v_1i+m₂v_2i = (m₁+m₂)v_f

m₁v₁i+m₂v₂i/v_f = m₁+m₂

∴ m₂ = ⌈m₁v_1i+m₂v_2i/v_f⌋- m₁

=⌊ (7100 kg)(12.0 m/s)+(m₂)(0 m/s) / 4.60 m/s⌋ - 7100 kg

= (18521.73kg)-(7100 kg)

= 11421.73 kg

m₂ ≈11422 kg

Mass of the second car is 11422 kg.