Sliding on the ice Alice and Bob are standing 5 m apart on the ice. A bag rests
ID: 776901 • Letter: S
Question
Sliding on the ice Alice and Bob are standing 5 m apart on the ice. A bag rests next to Alice. Alice slides the bag along the ice at 2 m/s to Bob who catches it when it arrived. You are asked to describe this scene in terms of conservation of momentum. Alice, Bob, and the bag have mass MA 60 kg, MB-70 kg, and Mba,-10 kg. At the moment when Alice pushes the bag, is there a net force on Alice, a net force on the bag, or a net force on Bob? Are these forces internal or external? What is the total net force? In the space below, draw Alice, the bag, and Bob when the bag is half way between them. Indicate their velocities on the sketch: vA, vB, Vbag. Use conservation of momentum to find vA in m/s?Explanation / Answer
a)When Alice pushes the bag there is a net force on bag and equal and opposite force on Alice as well.
b) These forces are internal force of Alice and bag system
c) The net force on the system is zero as the two forces are equal and opposite in direction.
d) Va*ma + vbag*mbag = 0
=> va = - vbag*mbag /va = - 2 * 10 / 60 = - 0.33 m/s
e) When Bob catches the bag there is a net force on Bob, equal and opposite force on the bag. The net force on Bob and bag system is zero.
f) These forces are internal forces of Bob bag system.
g) Vbag * mbag = vb+bag(mbag + mb)
Vb+bag = (Vbag * mbag) / (mbag + mb) = 2*10 / (10+70) = 0.25 m/s
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