Simple Harmonic Motion Self Test

Question 1

A large mass bobs up and down on a heavy spring. Initially the mass is at the top 20cm above its lowest position. The magnitude of its maximum speed is 31cm/s.

What is the amplitude for this motion?

A.  10cm
B.  20cm
C.  31cm
D.  40cm
E.  62cm   

What is the angular frequency for this motion?

A. 0.00πrads1
B. 0.25πrads1
C. 0.50πrads1
D. 0.75πrads1
E. 1.0πrads1

A. 0.00πrads1 - No. If the speed is given by v(t)=ωAsin(ωt) what is its maximum value?
B. 0.25πrads1 - No. If the speed is given by v(t)=ωAsin(ωt) what is its maximum value?
C. 0.50πrads1  - No. If the speed is given by v(t)=ωAsin(ωt) what is its maximum value?
D. 0.75πrads1  - No. If the speed is given by v(t)=ωAsin(ωt) what is its maximum value?
E. 1.0πrads1 - Correct!

v=ωAsinωt

Maximum value when sin=1

|vmax|=ωA

ω=|vmax|/A=31/10=3.1=1.0πs1

 

Quesstion 2

A large mass bobs up and down on a heavy spring. Initially it is at the top. It achieves its maximum downward velocity of 94cms1 in 0.25s from its release.

What are the period, angular freuqnecy, and amplitude for this motion?

T=

A. 0.25s
B. 0.5s
C. 0.75s
D. 1.0s
E. 2.0s

A. 0.25s - No. It hasnt gone through a full cycle.
B. 0.5s - No. It hasnt gone through a full cycle.
C. 0.75s - No. It hasnt gone through a full cycle.
D. 1.0s - Correct!
E. 2.0s - No. It has gone more than one full oscillation.

 

ω=

A. 0.00πrads1 
B. 0.50πrads1 
C. 1.0πrads1
D. 1.5πrads1 
E. 2.0πrads1 

A. 0.00πrads1 - No that is not correct. What is the relationship between ω and T?
B. 0.50πrads1 - No that is not correct. What is the relationship between ω and T?
C. 1.0πrads1 - No that is not correct. What is the relationship between ω and T?
D. 1.5πrads1 - No that is not correct. What is the relationship between ω and T?
E. 2.0πrads1 - Correct!

ω=2π/T=2π/1=2πs1 

 

A=

A. 15.0cm
B. 23.0cm
C. 94.0cm
D. 156cm
E. 188cm

A. 15.0cm - Correct!
B. 23.0cm - No. What is the expression for the maximum velocity?
C. 94.0cm - No. What is the expression for the maximum velocity?
D. 156cm - No. What is the expression for the maximum velocity?
E. 188cm - No. What is the expression for the maximum velocity?

vmax=ωA
A=vmax/ω=94/2π=15cm

 

Question 3

A large mass bobs up and down on a heavy spring. At first, it is seen moving up with a maximum velocity of 47cm/s. When it is 8.7cm above the central position, its speed is half its maximum value.

What are the amplitude, and angular frequency  for this motion?
 
 
A=

A.  5.0cm
B.  10cm
C.  15cm
D.  20cm
E.  25cm

A. 5.0cm - No. That is not correct. What are the expressions for the velocity and the maximum velocity?
B. 10cm - Correct!
C. 15cm - No. That is not correct. What are the expressions for the velocity and the maximum velocity?
D. 20cm - No. That is not correct. What are the expressions for the velocity and the maximum velocity?
E. 25cm - No. That is not correct. What are the expressions for the velocity and the maximum velocity?

v=ωAsinωt
vmax=ωA=47

v=47sinωt

23.5=47sinωt
sinωt=1/2
ωt=30

x=Acosωt
8.7=Acos30=0.866

A=8.7/0.866=10cm

 

ω=

A. 0.00πrads1 
B. 0.50πrads1 
C. 1.0πrads1
D. 1.5πrads1 
E. 2.0πrads1 

A. 0.00πrads1 - No. What is the relation for vmax?
B. 0.50πrads1 - Correct!
C. 1.0πrads1 - No. What is the relation for vmax?
D. 1.5πrads1 - No. What is the relation for vmax?
E. 2.0πrads1 - No. What is the relation for vmax?

vmax=ωA

but A=10

ω=47/10=0.75(2π)