Refer to the diagram when answering the next three questions. Two hockey pucks a

Question

Refer to the diagram when answering the next three questions. Two hockey pucks are at rest on a frictionless horizontal table. The diagram is a top view. Puck 1 has four (4) times the mass of Puck 2. The pucks are pushed by two equal and constant forces that continue pushing all the way across the table to the finish line. Which puck will reach the finish line first? 1 2 They will both reach the finish line at the same time. Too little information to answer. Which puck will have the greater kinetic energy upon reaching the finish line? 1 2 They both have the same amount. Too little information to answer. Now suppose there is friction between the table and the pucks, and the pucks have the same coefficient of kinetic friction. Which puck will have the greater kinetic energy upon reaching the finish line? 1 2 They both have the same amount. Too little information to answer

Explanation / Answer

(8)

t = x/v ..(1)

x = distance travelled is same in both cases.

v = velocity.

F = m*a

a = F/m

v^2 = v0^2+2*a*x, herev0 = 0

v^2 = 2*a*x = 2*(F/m)*x

hense, v2/v1 = 2 ..(2)

equation (1) and (2) shows, pluck 2 will reach earlier.

(9)

Kinetic energy of pluck 1.

KE1 = 1/2*4*m*v^2

Kinetic energy of pluck 2.

KE2 = 1/2*m*4*v^2

Hence,

KE1 = KE2

Here mass of pluck 1, m1 = 4*m, mass of pluck 2 = m.

Vel. of pluck 1, v1= v, velocity of pluck 2, v2 = 2*v.

(3)

Friction force = co.eff. of friction * normal force

= mu*m*g

Energy dissipation due to friction force:

=mu*m*g*x

For 1st pluck, m1 = 4m, so energy dissipation is more.

So in the end, while reaching the finishing line, pluck 2 will have more KE.

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