# Determine how long puck takes to cross ice

• j1249
No. In the vertical direction, the weight of the puck, mg, acts down. Since the puck is assumed to stay in contact with the ice, it is not moving vertically. So from equilibrium and Newton's first law, if the weight acts down, some other force must act up to balance it. This is the normal force in this situation (F_n), the upward force of the ice on the puck. So, F_n = ma.

#### j1249

i have no clue where to begin to solve this problem. Can anyone help me out and get me started please and thanks.

A hockey puck, sliding on an outdoor rink, has a velocity of 19 m/s forward when it suddenly hits a rough patch of ice that is 5.1 m across. Assume that the coefficient of kinetic friction between the puck and the rough ice is 0.47. Determine the time it takes the puck to clear the rough ice.

j1249 said:
i have no clue where to begin to solve this problem. Can anyone help me out and get me started please and thanks.

A hockey puck, sliding on an outdoor rink, has a velocity of 19 m/s forward when it suddenly hits a rough patch of ice that is 5.1 m across. Assume that the coefficient of kinetic friction between the puck and the rough ice is 0.47. Determine the time it takes the puck to clear the rough ice.
Are you familiar with
1. Newton's laws and the Kinematic motion equations? or
2. the Work-Energy Theorem?
Start by choosing one of these methods, and then please show your attempt at a solution.

yes I'm aware of Newtons laws and the kinematic motion equations but how do i go for solving for Fn so i can solve for Ff? Like, i could do Fg=mg to solve for Fn, but i don't have m so i can't do that equation.

i believe i no how to solve this question, but only if i had mass, which i dont

j1249 said:
i believe i no how to solve this question, but only if i had mass, which i dont
Maybe you don't need to know it. Try Newton's law and see what happens.

i have tried, but i am completely lost and confused

j1249 said:
i have tried, but i am completely lost and confused

What is the nornal force in terms of m? Write it down with the letters. What is the friction force in terms of m? Write it down with letters. Is the friction force the net force acting on the puck in the x direction? If so, F_net=ma, solve for a.

okay thanks but how do i figure out normal force in terms of m? it gives me absolutly no values besides the ones in the question

n [tex ]

meiso, that's what i would like to know to lol :)

j1249 said:
okay thanks but how do i figure out normal force in terms of m? it gives me absolutly no values besides the ones in the question
You may have already figured out the normal force in terms of m, in your 2nd post above.

so its zero?

j1249 said:
so its zero?
No. In the vertical direction, the weight of the puck, mg, acts down. Since the puck is assumed to stay in contact with the ice, it is not moving vertically. So from equilibrium and Newton's first law, if the weight acts down, some other force must act up to balance it. This is the normal force in this situation (F_n), the upward force of the ice on the puck. So, F_n = ______??