susan_khan
Homework Statement:
A 0.045 kg golf ball is hit by a driver. The head of the driver has a mass of 0.15 kg, and travels at a speed of 56 m/s before the collision. The ball has a speed of 67 m/s as it leaves the clubface. What is the speed of the head of the driver immediately after the collision?
Relevant Equations:
m1v1+m2v2 = m1v1f + m2v2f
vi1 +v1f = V2i +v2f
A 0.045 kg golf ball is hit by a driver. The head of the driver has a mass of 0.15 kg, and travels at a speed of 56 m/s before the collision. The ball has a speed of 67 m/s as it leaves the clubface. What is the speed of the head of the driver immediately after the collision?

I'm not sure where I'm going wrong but I first started off with this equation: m1v1+m2v2 = m1v1f + m2v2f. I was able to solve for v1f by using this equation and substituting it back into the main problem. (vi1 +v1f = V2i +v2f which equals 11 + v1f = v2f). After substuting this equation into the main equation I got v1f as 50.1 m/s and after subbing this number into this equation 11 + v1f = v2f I got v2f as 61.1 m/s. However the textbook says the answer is 36 m/s. What should I do?

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Homework Statement:: A 0.045 kg golf ball is hit by a driver. The head of the driver has a mass of 0.15 kg, and travels at a speed of 56 m/s before the collision. The ball has a speed of 67 m/s as it leaves the clubface. What is the speed of the head of the driver immediately after the collision?
Relevant Equations:: m1v1+m2v2 = m1v1f + m2v2f
vi1 +v1f = V2i +v2f

A 0.045 kg golf ball is hit by a driver. The head of the driver has a mass of 0.15 kg, and travels at a speed of 56 m/s before the collision. The ball has a speed of 67 m/s as it leaves the clubface. What is the speed of the head of the driver immediately after the collision?

I'm not sure where I'm going wrong but I first started off with this equation: m1v1+m2v2 = m1v1f + m2v2f. I was able to solve for v1f by using this equation and substituting it back into the main problem. (vi1 +v1f = V2i +v2f which equals 11 + v1f = v2f). After substuting this equation into the main equation I got v1f as 50.1 m/s and after subbing this number into this equation 11 + v1f = v2f I got v2f as 61.1 m/s. However the textbook says the answer is 36 m/s. What should I do?
Use
m1v1+m2v2 = m1v1f + m2v2f
without dropping the masses. That's what you should do.

susan_khan
Use
m1v1+m2v2 = m1v1f + m2v2f
without dropping the masses. That's what you should do.
Thank you for replying, but when solving I didn't drop the masses I just substituted 11 + v1f = v2f into this equation m1v1+m2v2 = m1v1f + m2v2f after inputting the values.

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Thank you for replying, but when solving I didn't drop the masses I just substituted 11 + v1f = v2f into this equation m1v1+m2v2 = m1v1f + m2v2f after inputting the values.
Where does 11 + v1f = v2f come from? Why isn't v1f multiplied by m1 and v2f multiplied by m2? Please show your solution from its beginning, not just the middle part of it.

susan_khan
Where does 11 + v1f = v2f come from? Why isn't v1f multiplied by m1 and v2f multiplied by m2? Please show your solution from its beginning, not just the middle part of it.
m1v1+m2v2 = m1v1f + m2v2f
(0.045)(67)+(0.15)(56) = 0.045v1f + 0.15v2f
3.015 + 8.4 = 0.045v1f + 0.15v2f
Before continuing I used this equation to solve for v1f
vi1 +v1f = V2i +v2f
67 + v1f = 56 +v2f
67 - 56 + v1f = 56 - 56 +v2f
11 + v1f = v2f
Sub this equation in:
3.015 + 8.4 = 0.045v1f + 0.15v2f
11.415 = 0.045v1f + 0.15(11 + v1f)
11.415 = 0.045v1f + 1.65 + 0.15v1f
11.415 -1.65 = 0.045v1f + 0.15v1f
9.765/0.195 = 0.195v1f/0.195
v1f = 50.1 m/s
Solve for v2f:
11 + 50.1 = v2f
v2f = 61.1 m/s

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m1v1+m2v2 = m1v1f + m2v2f
(0.045)(67)+(0.15)(56) = 0.045v1f + 0.15v2f

Stop here.
At this point you figured out that you needed one more equation and you invoked this
vi1 +v1f = V2i +v2f
without explanation or justification. It is a bogus equation. The fact is that v1f is known. Read the problem carefully to see what it is. Put it in the momentum conservation equation and solve for v2f.

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vi1 +v1f = V2i +v2f
This equation is only for the case of a perfectly elastic collision. The more general form, "Newton's Experimental Law", includes a coefficient of restitution.

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Is golf a sport played by hitting balls in motion?

SammyS and nasu
susan_khan
At this point you figured out that you needed one more equation and you invoked this
vi1 +v1f = V2i +v2f
without explanation or justification. It is a bogus equation. The fact is that v1f is known. Read the problem carefully to see what it is. Put it in the momentum conservation equation and solve for v2f.
I tried rereading the problem but I'm still unable to figure out the value for v1f. Could it be 0?