Polly is pushing a box across the floor with a force of 30n the force of gravity is -8n and the normal force is 8n which value could describe the force of friction if polly could not move the box a. -30n b. -8n c. 8n d. 30n

A)

Explanation:

As we know that box is not moving on the floor

so here net force on the box must be balanced

so in horizontal direction as well as in vertical direction net force must be zero

so we can say in vertical direction we have two forces

1) Normal force

2) weight

so we have

similarly in horizontal direction we have

1) Applied force

2) friction force

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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.