If there is friction on this problem then the first box would also experience a reduction in velocity making this a calculus problem. You cannot calculate the frictional force without more information. The second question implies that the third question should be solved by using forces, but the coefficient of friction is missing. Work-energy is not possible.
NEW FILE: WS: Momentum and Motion
In Honors and Regents Physics
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If there is friction on this problem then the first box would also experience a reduction in velocity making this a calculus problem. You cannot calculate the frictional force without more information. The second question implies that the third question should be solved by using forces, but the coefficient of friction is missing. Work-energy is not possible.