Question

5) A block of mass m slides without friction on a table with speed v. It hits and compresses a spring of force constant k by a distance l. The spring then expands again ejecting the block in the opposite direction as it was originally traveling. Neglecting the mass of the spring, what is the speed of the object after it is ejected by the spring?Select one:A. 4vB. vC. v/2D. 2v

Answer 1

Given data:

* The mass of the block is m.

* The initial velocity of the block is v.

Solution:

According to the law of conservation of momentum,

`p_f=p_i`

where p_f is the final momentum and p_i is the initial momentum,

The initial momentum of the block is,

`p_i=mv`

Thus, the final momentum of the block is,

`\begin{gathered} p_f=mv \\ mv_f=mv \end{gathered}`

where v_f is the final velocity of the block,

`v_f=v`

Thus, the final momentum of the block is v.

Hence, option B is the correct answer.