Agirl of mass mg is standing on a plank of mass mp. both are originally at rest on a frozen lake that constitutes a frictionless, flat surface. the girl begins to walk along the plank at a constant velocity vgp to the right relative to the plank. (the subscript gp denotes the girl relative to plank. use any variable or symbol stated above as necessary.)

1.) what is the velocity vpi of the plank relative to the surface of the ice?

2.) what is the girl's velocity vgi relative to the ice surface?

any understanding this would be appreciated.

Part a)

Part b)

Explanation:

As we know that there is no external force on the system of girl and plank

so we will say that total momentum of girl and plank will remains conserved

so we will say

now here we know that girl move with respect to plank with speed

now let say that the plank moves with speed v opposite to the motion of girl

so we have

Part b)

also the speed of girl with respect to the ice surface is given as

-4 on

note: the given question is incomplete.

complete question is given below.

which is an example of kinetic energy?

a. the energy stored in ethanol  

b. a hockey puck sliding across the ice  

c. a compressed spring  

d. a ball sitting at the top of a ramp

solution: the kinetic energy is the energy posses by the virtue of the motion of the object.

in the given options, a, c and d are the example of potential energy because it is the energy posses by the virtue of the rest of the object. but option b has the kinetic energy as the object is in motion.

hence, a hockey puck sliding across the ice   is the apex example of kinetic energy.

so, the option (b) a hockey puck sliding across the ice   is the correct option.