Assignment
Dynamics Lessons
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University:
Jackson College -
Course:
PHY 231 | College Physics I Academic year:
2024
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Views:
197
Pages:
117
Author:
Rigoberto Sheppard
9. A net force of 6.6 N East acts on a 9.0 kg object. The object accelerates uniformly from rest to a velocity of 3.0 m/s east. A) How far did the object travel while accelerating? B) What is the time of the acceleration? (6.1 m [E], 4.1 s)
10. A force of 5.0 N East and a force of 6.7 N East act on an 8.0 kg object. What is the acceleration of this object? (1.5 m/s² [E])
11. A force of 22.0 N East and a force of 25.0 N South act on a 4.2 kg cart. What is the acceleration caused by these forces? (7.9 m/s² 49° S of E)
7. If your weight is force created by gravity on your body, and therefore is the Earth pulling you down, what is the reaction force?
You pull up on the Earth.
8. There is nothing in outer space for rocket exhaust gasses to push against. How then can a rocket accelerate in outer space?
The rocket pushes out the gases and the gases push back on the rocket.
9. No matter how hard a horse pulls on a cart, the cart must pull back with exactly the same force according to Newton’s Third Law. How can a cart pull a horse? (For this question assume the horse and cart are on level ground.)
Exerts an equal & opposite reaction force, but wheels decrease the force needed to do work (accelerate the wagon)
10. A bug splatters on a fast-moving car’s windshield. Is the force on the car from the bug the same as the force on the bug from the car? Explain.
[F_1 = F_2]
Mass is so tiny in comparison to car that acceleration is extremely high (very high impulse causes damage to bug!)
11. Three blocks on a frictionless horizontal surface are in contact with each other. A force of 100 N is applied to block 1. Each block has a mass of 10.0 kg.
A) Determine the acceleration of the system. (+3.33 m/s²)
B) Determine the force that each box exerts on its neighbor.
[F_{1\rightarrow2} = F_{2\rightarrow3} = 67 N]
A) ΣF = ma
100 = 30a
a = 3.33 m/s²
B) F₁→₂ = F₂→₃ = (20)(3.3)
= 67 N
ΣF = (10)(3.3)
= 33 N
F₂→₃
12. Two crates, of mass 80 kg and 110 kg, are in contact and at rest on a horizontal surface. A 650 N force is exerted on the 80 kg crate. If the coefficient of friction is 0.20, calculate:
A) The acceleration of the system (1.46 m/s^2)
B) The force that each crate exerts on the other. (376 N)
ma = Fa + Ff
190a = 650 + (-0.20)(190)(9.8)
13. While standing on a horizontal, frictionless surface, two students push against each other. Angela has a mass of 38 kg and, during the push, is accelerating east at a rate of 0.60 m/s². If Bob is accelerating west during the push at a rate of 0.75 m/s², what is his mass? (30 kg)
F = ma
F = (38)(0.6) = 22.8 N = F2
-22.8 = m(-0.75)
m = 30 kg
14. While standing on a horizontal frictionless surface, a 65.0 kg student pushes against a wall with a force of 148 N west for 0.250 s. Calculate the velocity of this student at the end of the 0.250 s. (0.569 m/s [E])
F = ma
148 = 65.0a
a = 2.28 m/s²
a = (vf - vo) / t
2.28 = (vf - 0) / 0.250
vf = 0.569 m/s [E]
Physics 12 - The Physics of Inclined Planes
In physics, we call any tilted surface an inclined plane. As long as the force of friction is not greater than the component of gravity parallel to the surface, the object will slide down the surface.
The rate in which the object will accelerate down an inclined plane depends on how tilted the inclined plane is.
Assuming no friction:
two inclined planes with different angles, showing acceleration will be greater for the steeper slope
The object will accelerate according to Newton's Laws of motion: unbalanced forces acting on the object.
We already know that the normal force is always perpendicular to the surface and that we can use component of F_g to determine the normal force acting on an object on an inclined plane.
[Image showing a block on an inclined plane with forces labeled: F_g (force of gravity), F_N (normal force), and F_|| (component of F_g parallel to the surface)]
F_|| is opposed to the normal force and therefore balances the normal force.
However, we know that an unbalanced force causes the object to accelerate down the inclined plane.
[Image showing a block on an inclined plane with forces labeled: F_g, F_N, F_||, and F_⊥]
F_|| is not balanced by any other force.
Therefore, F_|| results in acceleration in that direction.
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