Force and Acceleration/Force of Friction and Air Resistance. 5 Basic Questions.

[Underdog_85]

Q1: Assuming friction force to be negligibly small, what will be the acceleration in m/s^2 of a 45kg skater when propelled by a force of 250N?
My attempt
Data:
F-250N
m-45kg
a-m/s^2

Formula:
F=ma
a=F/m
a=250N/45kg
a=5.555
a=5.6m/s^2
Q2: a 0.5kg mass on a horizontal frictional free table is accelerated by a force from a string passing over a pulley and attached to a mass of 1.5kg hanging vertically.

My attempt
Data:
m-0.5kg
hanging m-1.5kg

formula:
F=F1+F2
F=0.5kg+1.5kg=2.0kg
F=ma
F=2.0kg(9.80m/s^2)
F=19.6 rounded to 20N

My attempt at B)
Data:
F=19.6N
m=2kg
a=?m/s^2?

Formula:
F=ma
a=F/m
a=19.6N/2kg
a=9.8 rounded to 10m/s^2
Q3: A 1200kg truck is moving at 108km/h and stops within a distance of 91m
a)What is the acceleration?

My attempt
Data:
m-1200kg
Vi-108km/h--->converted to 30m/s
Vf-0
s-91m

Formula:
2as=Vf^2+Vi^2
a=Vi^2/2s
a=(30m/s)^2/2(91m)
a=900m^2/s^2/182m
a=-4.9m/s^2(negative because it decelerated)

My attempt at part B)What is the coefficient of friction?
Formula:
Ff=uFn
u=Ff/Fn
u=4.9m/s^2/1200kg
u=0.00408
Q4: you are pulling a 3.0slug crate and a sliding friction is known to be 55lb. what is the acceleration o the crate when the pulling force is?
a)55lb, b)75lb and c)105lb

My attempt at a)
Date:
m: 3.0Slug
F:55lb
a:?m/s^2?

Formula:
F=ma
a=F/m
a=55lb/3.0slug
a=18ft/s^2

My attempt at part b)
Data:
m: 3.0slug
F: 75lb
a: ??

formula:
F=ma
a=F/m
a=75lb/3.0slug
a=25ft/s^2

My attempt at part c)
Data:
m: 3.0slug
F:105lb
a-??

Formula:
F=ma
a=F/m
a=105lb/3.0slug
a=35ft/s^2
Q5: During a training exercise, Brian who weighs 75kg skydives and parachutes from a stationary helicopter. What is the acceleration when the air drag is a)500N, b)1500N, and c)Equal to his weight

My attempt at a)
Data:
Fw:75kg
g:-9.80m/s^2
m: 500N
a=?

Formula:
F=ma
a=F/m
a=500N/75kg
a=6.66m/s^2

My attempt at b)
Formula:
a=F/m
a=1500N/75kg
a=20m/s^2

My attempt at c)
Formula
a=f/m
a=75N/75kg
a=1 m/s^2
first of all I want to thank anyone that gives their time and effort to help me do this homework that is due very soon. I don’t think I understand it very well and I am start to get really worried. Secondly, if you notice any problems, can you please show me how to do it? Id appreciate any help I can get. Thanks a ton people.

 

[willem2]

Q1: ok

Q2; you didn't copy question A. F=19.6 N is wrong however (and F=2.0kg is wronger)
Let T be the tension in the rope, and then find the net force on both blocks
from gravity and this unknown tension. Then use F=ma for both blocks, and the fact
that a is the same for both blocks to find T.

Q3-a: The answer is OK. You should have been using 2as=Vf^2-Vi^2 and then a would have
become negative by itself. The sign of a also depends on what direction is chosen as
the positive direction. Here it's the direction that the car drives, but that isn't always the case.
Q3-b: 4.9 m/s^2 isn't a force and neither is 1200 kg. What are the forces?
Q4: I don't do slugs, but you need to find the net force, which includes the friction force that is opposite to the pulling force.
Q5: You need to find the net force here as well. In physics weight is a force, the force of gravity, and it is equal to the mass times the acceleration of gravity mg with g = 9.8 m/s^2
so the weight of the person is 735N and not 75 kg.

 

[kerimek]

Hello there, it seems like you have put in a lot of effort in attempting these questions. I will be happy to provide some feedback and help you understand the concepts better.

For Q1, your calculation for acceleration is correct. It is important to note that the unit for acceleration is m/s^2 and not just m/s.

For Q2, your calculation for the total force is correct. However, for part B, the given data does not specify the mass of the hanging mass. So, we cannot calculate the acceleration without that information. We also need to know the direction of the acceleration (whether it is positive or negative) in order to accurately answer the question.

For Q3, your calculation for acceleration is correct. It is important to remember that the unit for acceleration in this case would be m/s^2 and not just m/s. For part B, your calculation for the coefficient of friction is correct. However, it is important to mention the unit for the coefficient of friction, which is dimensionless.

For Q4, your calculations for acceleration for all three parts are correct. However, it is important to remember that the unit for acceleration in this case would be ft/s^2 and not just ft/s.

For Q5, your calculations for acceleration for all three parts are correct. However, it is important to mention the unit for acceleration, which is m/s^2.

Overall, your understanding of the concepts seems to be good. However, it is important to remember the units for each variable and to mention them in your answers. Also, make sure to double check the given data and the units to avoid any errors in your calculations. Keep up the good work!