Question

Two identical ice hockey pucks, labeled A and B, are sliding toward each other at speed v. Which one of the following statements is true concerning their momenta and kinetic energies?
a. p(A) = p(B) and KEA= KEB
b. pA= - pB and KEA= -KEB
c. pA= -pB and KEA= KEB
d. pa= pb and KEA =- KEB

Answer 1

Answer:

C. $p_{A} = -p_{B}$ and $K_{A} = K_{B}$.

Explanation:

The two hockey pucks travels in opposite sides with velocities of same magnitude, by definitions of linear momentum and translational kinetic energy:

Linear momentum

Hockey puck A

$p_{A} = m\cdot v$ (1)

Hockey puck B

$p_{B} = -m\cdot v$ (2)

$p_{A} = -p_{B}$

Translational kinetic energy

Hockey puck A

$K_{A} = \frac{1}{2}\cdot m\cdot (v)^{2}$

$K_{A} = \frac{1}{2}\cdot m \cdot v^{2}$ (3)

Hockey puck B

$K_{B} = \frac{1}{2}\cdot m\cdot (-v)^{2}$

$K_{B} = \frac{1}{2}\cdot m \cdot v^{2}$ (4)

$K_{A} = K_{B}$

Hence, the correct answer is C.