(10%) Problem 7: A young 4 kg ice hockey goalie, originally at rest, catches a 0
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(10%) Problem 7: A young 4 kg ice hockey goalie, originally at rest, catches a 0.16 kg hockey puck slapped at him at a speed of 33 m/s. In this problem, take the original direction of the puck as positive. 50% Part (a) Suppose the goalie and the ice puck have an elastic collision and the puck is reflected back in the direction from which it came. What would the final velocity of the puck, in meters per second, be in this case? 50% Part (b) Suppose the goalie and the ice puck have an elastic collision and the puck is reflected back in the direction from which it came. What would the final velocity, in meters per second, of the goalie be in this case? Grade Summary Deductions 090Explanation / Answer
m1 = 47 kg
initial speed u1 = 0
m2 = 0.16 kg
its initial speed u2 = 33 m/s
from conservation of momentum
m1*u1 + m2*u2 = m1*v1 + m2*v2
47*0 + 0.16*33 = 47*v1+0.16*v2
47*v1+0.16*v2 = 5.28 .............eq(1)
since it is elastic collision
v2 -v1 = u1 -u2
v2 - v1 = - 33 ...........eq(2)
substituting eq(2) in eq(1)
47*v1+0.16*(v1 - 33) = 5.28
47.16*v1 = 10.56
v1 = 0.22 m/s
put the value of v1 in eq(2)
v2 = -32.77 m/s
so
final speed of hockey goalie is 0.22 m/s
final speed of puck is -32.77 m/s
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