The following two questions (4 and 5) pertain to a 200g hockey puck that is laun

Question

The following two questions (4 and 5) pertain to a 200g hockey puck that is launched up a ramp inclined at a 30° angle above the horizontal. The coefficients of static and kinetic friction between the puck and the ramp are µs = 0.305 and µk = 0.300, respectively, and the puck's initial velocity at the base of the ramp is 3.8m/s.

A) How much time does it take for the puck to reach its highest point on the ramp (before it momentarily stops and begins sliding back down)?

a.) 0.1s

b.) 0.2s

c.) 0.3s

d.) 0.4s

e.) 0.5s

B)What is the puck’s acceleration as it slides back down the ramp?

a.) 2.35m/s2 , directed up the ramp

b.) 2.35m/s2 , directed down the ramp

c.) 4.90m/s2 , directed down the ramp

d.) 7.25m/s2 , directed down the ramp

e.) 7.25m/s2 , directed up the ramp

Explanation / Answer

From the kinematic equations

v = u + at here u = 3.8 m/s

a)When moving up the negative acceleration = g[ sin 30 + 0.3 cos 30] = 7.45 m/s^2

Therefore time taken is option e)0.5s

B)When moving down the acceleration is = g[ sin 30 - 0.3 cos 30] = 2.35m/s^2

Option b) 2.35m/s^2

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