Jean Blumer

2021-12-20

A550-N physics student stands on a bathroom scale in an elevator that is supported by a cable. The combined mass of student plus elevator is 850 kg. As the elevator starts moving, the scale reads 450 N.

(a) Find the acceleration of the elevator (magnitude and direction).

(b) What is the acceleration if the scale reads 670 N?

(c) If the scale reads zero, should the student worry? Explain.

(d) What is the tension in the cable in parts (a) and (с)?

stomachdm

Beginner2021-12-21Added 33 answers

Let the +y-axis be upward. The free-body diagrams for the elevator plus student and the student alone are shown in the figure below. The total mass of student plus elevator is

The normal force exerted by the scale on the student is denoted by n. By Newton's third law, this force is equal in magnitude to the downward pressure exerted by the student's feet on the scale (the scale reading), that is n represents the scale’s reading.

The mass of the student alone, whose actual weight is

(a)Application of the y-equation of Newton's second law,

The scale’s reading corresponds to

So the student, and thus the elevator, has an acceleration of magnitude 1.78 m/ s, which is directed downward.

(b) Repeating part (a) using the new scale reading,

which represents an acceleration of magnitude 2.14 m/s” and upward direction

(c) In case the scale's reading was zero, that isn = 0, we have

The elevator is in free fall...Trouble!

(d) To find the tension T in the cable, we must apply Newton's second law to the student plus elevator this time.

Application of

In part (a),

In part (c),

Yes, exactly! That is the trouble!

stomachdm

Beginner2021-12-22Added 33 answers

(a)

The equation of the forces acting on the student is:

where

Nis the normal reaction of the scale on the student mg is the weight of the student

a is the acceleration of the student

The scale reads 450 N, so this is the normal reaction:

Also, we know that the weight of the student is:

So we can find its mass:

So now we can solve eq.(1) to find the acceleration:

where the negative sign means the acceleration is downward.

(b)

Again, the equation of the forces is

where this time, the reading of the scale (and so, the normal reaction) is

Solving for the acceleration, we find

and the positive sign means the acceleration here is upward.

(c) Yes

Let's assume the scale is reading zero. In terms of forces, this means that the normal reaction on the student is zero:

N=0

So the equation of the forces simply becomes

mg =ma

Therefore the acceleration is

which means that the elevator is accelerating downward at 9.8m/s^{2} this means that the elevator is in free fall, so yes, the student should worry.

Let's now consider the equation of the forces on the elevator:

T-mg =ma(2)

where this time:

T is the tension in the cable

Solving for T,

(d) (b) 10149 N

Here we can use the same equation

where the only difference is that the acceleration is

Solving the equation for T, we find

(d) (c) 0

Again, same equation

But this time, the acceleration is

So, we find:

So, the tension in the cable is zero, since the elevator is in free fall.

2021-12-27

Step1

Given,

Weight of physics student = 550N

mass of elevator and student = 850kg

Step2

Step3

(a)

(b)

(c)

if scale read zero then elevator is going down with acceleration of 9.81

(d)

the temnsion in part (a)

tension in part (c)

Step 4

Answer:

(a) magnitude of acceleration is 1.78

(b)

magnitude of acceleration is 2.14

(C)

if scale read zero then elevator is going down with acceleration of 9.81

(d)

for part (a) 6825.5 N

for part (c) ON

Jazz Frenia

Skilled2023-05-28Added 106 answers

Andre BalkonE

Skilled2023-05-28Added 110 answers

Three identical blocks connected by ideal strings are being pulled along a horizontal frictionless surface by a horizontal force $\overrightarrow{F}$ The magnitude of the tension in the string between blocks B and C is T=3.00N. Each block has mass m=0.400kg.

What is the magnitude F of the force?

What is the tension in the string between block A and block B??We have: A golf ball of mass 0.045 kg is hit off the tee at a speed of 45 m/s. The golf club was in contact with the ball for $5.0\times {10}^{-3}$ s. Find (a) the impulse imparted to the golf ball,and (b) the average force exerted on the ball by the golf club

???A box is sliding with a speed of 4.50 m/s on a horizontal surface when, at point P, it encounters a rough section. On the rough section, the coefficient of friction is not constant but starts at .100 at P and increases linerly with distance past P, reaching a value of .600 at 12.5 m past point P. (a) Use the work energy theorem to find how far this box slides before stopping. (b) What is the coefficient of friction at the stopping point? (c) How far would the box have slid iff the friciton coefficient didn't increase, but instead had the constant value of .1?

?

The spring in the figure (a) is compressed by length delta x . It launches the block across a frictionless surface with speed v0. The two springs in the figure (b) are identical to the spring of the figure (a). They are compressed by the same length delta x and used to launch the same block. What is the block's speed now?A spring gun's spring has a constant force k =400 N/m and negligible mass. The spring is compressed 6.00 cm and a ball with mass 0.0300 kg is placed in the horizontal barrel against the compressed spring.The ball is then launched out of the gun's barrel after the spring is released. The barrel is 6.00 cm long, so the ball leaves the barrel at the same point that it loses contact with the spring. The gun is held so the barrel is horizontal. Calculate the speed with which the ballleaves the barrel if you can ignore friction. Calculate the speed of the ball as it leavesthe barrel if a constant resisting force of 6.00 Nacts on the ball as it moves along the barrel. For the situation in part (b), at what position along the barrel does the ball have the greatest speed?

?A small rock with mass 0.12 kg is fastened to a massless string with length 0.80 m to form a pendulum. The pendulum is swinging so as to make a maximum angle of 45 with the vertical. Air Resistance is negligible.

?

a) What is the speed of the rock when the string passesthrough the vertical position?

b) What is the tension in the string when it makes an angle of 45 with the vertical?

c) What is the tension in the string as it passes through the vertical?

Calculate the actual mechanical advantage of a lever.

The change in internal energy of a system that has absorbed 2 kcal of heat and does 500 J of work is

A) 6400J

B) 5400J

C) 7860J

D) 8900JThe electric field 10 cm from a long wire is 2.4 kN/C. If wire carries uniform charge, what will be the field strength at 40 cm from the wire?

$A)0.6\text{}kN/C;\phantom{\rule{0ex}{0ex}}B)150\text{}N/C;\phantom{\rule{0ex}{0ex}}C)75\text{}N/C;\phantom{\rule{0ex}{0ex}}D)4.8\text{}kN/C$Read each statement below carefully and state, with reasons, if it is true or false : (a) The net acceleration of a particle in circular motion is always along the radius of the circle towards the centre (b) The velocity vector of a particle at a point is always along the tangent to the path of the particle at that point (c) The acceleration vector of a particle in uniform circular motion averaged over one cycle is a null vector

Two paths lead to the top of a hill. One is shorter and steeper and the second one is longer but less steep. For which of the two paths is the gain in potential energy more?

A) Path I

B) Path II

C) Same for both the paths

D) Data insufficientWhat does negative $\mathrm{\u25b3}G$ mean?

What is a lever.

The gravitational unit of force is_?

What do you mean by $1\mathrm{eV}$?