A block with a mass of 4 kg is hit by a 1.5 m long pendulum, which send the block 3.5 m along the track with a velocity
Posted: Mon May 09, 2022 5:48 pm
A block with a mass of 4 kg is hit by a 1.5 m long
pendulum, which send the block
3.5 m along the track with a velocity of 2.5
m/s.
The force of friction between the block and
the track is 0.55 N.
What is the mass of the pendulum?
MY WORK:
Step #1: Find the ET as it begins to move
ET = Ep + Ek
ET = (4 kg)(9.81N/kg)(0m)+1/2(4 kg)(2.5
m/s)2
ETA = 12.5 J
Step #2: Find the work done on the track
Wthermal = F𝜟d
Wthermal= (0.55N)(3.5m)
Wthermal = 1.925J
Step #3: Find the total Energy
ET = W = Ff 𝜟d
ET = ET + Ethermal
ET = 12.5 J + 1.925 J
ET = 14.425 J
Step #4: Find the mass
ET = Ep + Ek
14.425 J = (m)(9.81N/kg)(0m) +
1/2(x)(2.5m/s)2
14.425 J = ½(x)(6.25)
14.425 J = 3.125x
x = 4.62 kg
BUT the answer is 2.4 kg.... what have I done wrong?
pendulum, which send the block
3.5 m along the track with a velocity of 2.5
m/s.
The force of friction between the block and
the track is 0.55 N.
What is the mass of the pendulum?
MY WORK:
Step #1: Find the ET as it begins to move
ET = Ep + Ek
ET = (4 kg)(9.81N/kg)(0m)+1/2(4 kg)(2.5
m/s)2
ETA = 12.5 J
Step #2: Find the work done on the track
Wthermal = F𝜟d
Wthermal= (0.55N)(3.5m)
Wthermal = 1.925J
Step #3: Find the total Energy
ET = W = Ff 𝜟d
ET = ET + Ethermal
ET = 12.5 J + 1.925 J
ET = 14.425 J
Step #4: Find the mass
ET = Ep + Ek
14.425 J = (m)(9.81N/kg)(0m) +
1/2(x)(2.5m/s)2
14.425 J = ½(x)(6.25)
14.425 J = 3.125x
x = 4.62 kg
BUT the answer is 2.4 kg.... what have I done wrong?