Physics Lab Exam 2

Which statement is true for a centripetal force?

This is one of the regular forces that acts on a moving object to keep the object on a circular path and is always pointed to the center of the circle.

Why did we “zeroed” the force sensor in vertical-hanging position with the bob mounted to correctly do the experiment? (Note: During the oscillations of the centripetal force pendulum the motion came momentarily at rest at the extreme position on either side of the swing.)

To avoid counting the weight in measuring the centripetal force at the bottom of the swing.

You might have noted that for most of the oscillations during the experiment your measured centripetal force at the bottom of the swing – both calculated from measured angular speed or reading directly from the measured force graph – was somewhat less than the theoretical result provided on the last column of the data table. What is the most possible reason for this to happen?

Because since in reality there is some friction on the axel of the swing and there is the air resistance, the speed of the pendulum has become somewhat slower than what the theory assumed.

To measure its spring constant, you mounted a few masses from a vertically hanging spring and measured the spring’s stretches. The stretch versus weight graph passed closely through the origin. This is because:

The stretches were measured from the length of the freely hanging spring.

You measured the frequency of oscillation for a mounted mass by stretching the spring-mass system down to set it on simple harmonic oscillations. In setting this motion you might have noted that the measured frequency is insensitive to how far you stretched it (even though it was generally told not to stretch too much to avoid the mass flying away). Why?

Because frequency of oscillation is independent to the amplitude of oscillations. It depends on the mass and spring constant.

In the vertical simple harmonic motion studied in the experiment, which statement is correct?

The speed is at maximum and magnitude of acceleration is zero at the equilibrium position. But the speed is zero and magnitude of acceleration is maximum at either of topmost or bottommost position.

Resonance creation on a tight string was done by hanging a lighter and then a heavier mass. This change was carried out in order to:

Increase the wave speed on the string by increasing the mass.

Resonances in the string vibration were formed by tuning the frequency (f) of the vibrator. By hanging a 100-gram mass over a pulley to tighten a string of vibrating length L, a certain number (n) of bumps was formed for a frequency f_n around 60 Hz. Recall, the resonance frequencies f_n = n(v/2L). For a 200-gm mass and around the same 60-Hz frequency (f_n), the number of bumps n at resonance

Decreased because v increased

In the final part of the lab, the fundamental resonance was found by determining a certain resonance length of a both-end-open pipe using a 512-Hz tuning fork. What would happen if you used a tuning fork of higher Hz value?

The resonance length will decrease since the wavelength shortens with higher frequency.

While measuring the specific heat by calorimetry, the way done in the lab, you used a 20-gm of a metal (sample-1) initially at 100^o C to measure an equilibrium temperature of 30 ^o C, while the sample lost Q calories of heat. You repeated  the experiment with 20-gm of a different metal (sample-2) at 100^o C to equilibrate at 35^o C by releasing the same Q calories of heat. What can you conclude from these measurements?

The resonance length will decrease since the wavelength shortens with higher frequency.

You performed two separate latent heat experiments, each as done in the lab, with different amounts of ice samples but using the same calorimeter with same amount of warm water in it at the same temperature initially. Sample-1 entirely melted. But sample-2 could only melt partially and then stopped with no further change in temp.  You conclude:

Sample-2 was of larger amount while, both being ice, they have the same latent heat.

What is the fundamental difference between the specific heat and the latent heat?

The specific heat runs the show when the temperature of the matter changes while the latent heat does so when the matter changes its phase.