Question

A hockey puck of mass 0.245 kg leaves a hockey stick at a speed of 29 m/s. The coefficient of kinetic friction between the ice and puck is 0.080.

a) What is the acceleration of the puck once it leaves the stick?
b) How long will it take for the puck to stop?

Answer 1

Explanation:

(a) Since the puck is on a horizontal surface, the normal force is vertical. With a

y

=0, we see that

∑F

y

=ma

y

→n−mg=0 or n=mg

Once the puck leaves the stick, the only horizontal force is a friction force in the negative x direction (to oppose the motion of the puck). The acceleration of the puck is

a

x

=

m

∑F

x

=

m

−f

k

=

m

−μ

k

n

=

m

−μ

k

(mg)

=−μ

k

g

(b) Then v

xf

2

=v

xi

2

+2aΔx give the horizontal displacement of the puck before coming to rest as

Δx=

2a

x

v

xf

2

−v

xi

2

=

2(−μ

k

g)

0−v

i

2

=

2μ

k

g

v

i

2

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Answer 2

Answer:

a.μkg

b.v_i_2_

2μkg

Explanation:

a. Since the puck is on a horizontal surface, the normal force is vertical. With a

y

=0, we see that

∑F

y

=ma

y

→n−mg=0 or n=mg

Once the puck leaves the stick, the only horizontal force is a friction force in the negative x direction (to oppose the motion of the puck). The acceleration of the puck is

a

x

=

m

∑F

x

=

m

−f

k

=

m

−μ

k

n

=

m

−μ

k

(mg)

=−μ

k

g

b.Then v

xf

2

=v

xi

2

+2aΔx give the horizontal displacement of the puck before coming to rest as

Δx=

2a

x

v

xf

2

−v

xi

2

=

2(−μ

k

g)

0−v

i

2

=

2μ

k

g

v

i

2

hope this helps