Lab 7, Inelastic Collisions

I. Perfectly Inelastic Collisions

Lab 7, Inelastic Collisions03/19/2000

Courtesy of Chiung-Yuan Lin and Benli Young

Mass, Unit:( )

Glider with pin

Glider with plug

1. Prepare and weigh the gliders and all masses:

2. Set up timing photo-gates:

The length of Glider should be the total length which the photo-gate can detect.

Item	Glider with pin	Glider with plug	Average of two Gliders
Length, Unit:( )

3. Make measurements: (Just fill in the data)

One glider initially at rest, the other started by the launcher

The positive velocities are measured to the right.

You do all three cases and choose only one case to complete the whole row. Your sample calculation is not required here.

m₁

(kg)

m₂

(kg)

V_1i

(m/s)

V_2i

(m/s)

V_f

(m/s)

P_i

(kg-m/s)

P_f

(kg-m/s)

D P

(kg-m/s)

K_i

(Joul)

K_f

(Joul)

D K

(Joul)

´ 100%

Both gliders started by the launchers

You do all three cases, choose only one case to go through it to ´ 100% and write down your sample calculation.

m₁ (kg)	m₂ (kg)	V_1i (m/s)	V_2i (m/s)	V_f (m/s)	P_i (kg-m/s)	P_f (kg-m/s)	DP (kg-m/s)	K_i (Joul)	K_f (Joul)	DK (Joul)	´ 100%
											%
											%
											%

4. Answer the Additional Question I, (2 point)

Starting from the two equations on Page 43 of Phys40A, or Pages 45 and 46 of Phys2LA, derive an expression of DK only in terms of m₁, m₂, V_1i, V_2i. Then simplify your expression to prove that DK ³ 0 for any initial velocities. Your mathematical work stands one point. (0.5 points for your final answer) How can we make DK = 0? (0.5 points) Is it possible to perform the specific situation today? Why?

Hint:

m₁V_1i+m₂V_2i = (m₁+m₂)V_f, (a + b)² = a² + 2ab + b², and (a - b)² = a² - 2ab + b²

Also, remember that the velocity here is still a one-dimensional vector, which has two elements: magnitude and direction.

II. Other inelastic collisions

m (kg)	V_i (m/s)	V_f (m/s)	K_i (Joul)	K_f (Joul)	DK (Joul)	´100%
						%
						%
						%

2. Plot Graph "D K versus K_i".

3. Answer Question 2 on page 43: Is a constant fraction of energy lost, or is a fixed amount of energy lost?

Hint: Do not answer this question with a simple "YES" or "NO" or you loss 1 point. Use your Graph "DK versus K_i" to answer this question.

Samples of Part I. Perfectly Inelastic Collisions

Below is a sample when performing collisions with the “wax” glider initially at rest.

|v_1i| = 0.638(m/sec), |v_2i| = 0.000(m/sec), |v_f| = 0.303(m/sec)

Special option values - "collision Timer" Mode
Row	velocity	velocity
#	(m/sec)	(m/sec)
1	0.6376	0.3025
2	Error	0.2972

Carefully read the following remark when performing collisions by launching both gliders.

Special option values - "collision Timer" Mode
Row	velocity	velocity
#	(m/sec)	(m/sec)
1	0.5470	0.3862

Below is a sample when v_f goes back and forth.

|v_1i| = 0.547(m/sec), |v_2i| = 0.386(m/sec), |v_f| = 0(m/sec)

Below is a sample when v_f goes fast enough.

|v_1i| = 0.391(m/sec), |v_2i| = 0.468(m/sec), |v_f| = 0.0938(m/sec)

Special option values - "collision Timer" Mode
Row	velocity	velocity
#	(m/sec)	(m/sec)
1	0.3909	0.4677
2	Error	0.09375
3	Error	0.09110

Below is a sample when v_f goes too slow.

|v_1i| = 0.549(m/sec), |v_2i| = 0.468(m/sec), |v_f| = 0.0148(m/sec)

Special option values - "collision Timer" Mode
Row	velocity	velocity
#	(m/sec)	(m/sec)
1	0.5489	0.4678
2	Error	0.01483

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