Answer :
The minimum initial speed of the dart so that the combination makes a complete circular loop after the collision is 58.5 m/s.
Minimum speed for the object not fall out of the circle
The minimum speed if given by tension in the wire;
T + mg = ma
T + mg = m(v²)/R
tension must be zero for the object not fall
0 + mg = mv²/R
v = √(Rg)
Final speed of the two mass after collision
Use the principle of conservation of energy
K.Ef = K.Ei + P.E
¹/₂mvf² = ¹/₂mv² + mg(2R)
¹/₂vf² = ¹/₂v² + g(2R)
¹/₂vf² = ¹/₂(Rg) + g(2R)
vf² = Rg + 4Rg
vf² = 5Rg
vf = √(5Rg)
vf = √(5 x 2.8 x 9.8)
vf = 11.7 m/s
Initial speed of the dart
Apply principle of conservation of linear momentum for inelastic collision;
5v = vf(20 + 5)
5v = 11.7(25)
5v = 292.5
v = 58.5 m/s
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