Assignment 4.1 – Newtonian Mechanics/Forces

CONCEPTUAL QUESTIONS:

  1. State Newton’s 1st Law:
  1. State Newton’s 2nd Law:
  1. State Newton’s 3rd Law:
  1. What is the equation for Newton’s 2nd Law?
  1. Explain superposition and its relation to force.
  1. What is an inertial reference frame? (Give an example)
  1. What is an non-inertial reference frame? (Give an example)
  1. What is a force?
  1. What is friction? (Give an example)
  1. What is a tension force? (Give an example)
  1. How do you find the components of a force vector?
  1. How do you find the magnitude of a force vector?
  1. How do you find the angle of a force vector?
  1. A ball is released from a vertical height of 20 cm. It rolls down a “perfectly frictionless” ramp and up a similar ramp. What vertical height on the second ramp with the ball reach before it starts to roll back down?
  1. You push a ball to start it rolling along a “perfectly frictionless” surface.

a)How far will the ball roll?

b)Explain your answer for a) using Newton’s law of motion.

  1. When an athlete is preparing to throw a shot put, does the ball exert a force on the athlete’s hand equal and opposite to the force the hand exerts on the ball? Explain your answer.
  1. You have weighed yourself by stepping on a scale many times. How do you think a simple bathroom scale works?
  1. For a hit in baseball, compare the force exerted by the bat on the ball to the force exerted by the ball on the bat. Why do bats sometimes break?
  1. Suppose that the acceleration of an object is zero. Does this mean that there are no forces acting on it? (Give an example that supports your answer)
  1. If your textbook is in equilibrium, what can you say about the forces acting on it?

QUESTIONS:

(SUPER EASY MODE)

  1. A tennis racket hits a sand-filled tennis ball with a force of 4.0 N. While the 275 g ball is in contact with the racket, what is its acceleration?
  1. What is the acceleration of a 0.30 kg volleyball when a player uses a force of 42 N to spike the ball?
  1. What force would be needed to accelerate a 0.040 kg golf ball at 20.0 ?
  1. In the United States, people measure body weight in pounds. Imagine a person weighs 150 lb.

a)Convert the person’s weight in pounds to the international unit of force, newtons. To do so, use the following conversion equation:

Weight in newtons = (weight in pounds)(4.38 newtons per pound)

b)Use the person’s body weight, in newtons, and the equation

To calculate the person’s body mass (m), in kilograms.

  1. Carlo and Sara push on a desk in the same direction. Sara pushes with a force of 50 N, and Carlo pushes with a force of 40 N. What is the unbalanced force acting on the desk? (The unbalanced force on an object is sometimes called the total force, or net force, on an object.
  1. A vehicle is stuck in the mud. Four adults each push on the back of the vehicle with a force of 200 N. What is the combined force, due to tall four adults, on the vehicle?
  1. A baseball player throws a ball. While the 700.0 g ball is in the pitcher’s hand, there is a force of 125 N on it. What is the acceleration of the ball?
  1. During a football game, two players try to tackle another player. One player applies a force of 50.0 N to the east. A second player applies a force of 120.0 N to the north. What is the resultant force applied to the player being tackled? (Since force is a vector, you must give both the magnitude and direction of the force.)
  1. Bob exerts a 30.0 N force to the left on a box (m = 100.0 kg). Carol exerts a 20.0 N force on the same box, perpendicular to Bob’s force.

a)What is the net force on the box?

b)Determine the acceleration of the box?

  1. Three confused sleigh dogs are trying to pull a sled across the Alaskan snow. Alutia pulls east with a force of 35 N, Seward also pulls east but with a force of 42 N, and big Kodiak pulls west with a force of 53 N. What is the net force on the sled?
  1. You place a watermelon on a spring scale at the supermarket. If the mass of the watermelon is 4.0 kg, what is the reading on the scale?
  1. What is the net force acting on a 1.0 kg ball in free-fall?
  1. A car of mass 2300 kg slows down at a rate of 3.0 when approaching a stop sign. What is the magnitude of the net force causing it to slow down?

(MEDIUM)

  1. Taru and Reiko simultaneously grab a 0.75 kg piece of rope and begin tugging on it in opposite directions. If Taru pulls with a force of 16.0 N and the rope accelerates away from her at 1.25 , with what force is Reiko pulling?
  1. Marcos is playing tug-of-war with his cat using a stuffed toy. At one instant during the game, Marcos pulls on the toy with force of 22 N, the cat pulls in the opposite direction with a force of 19.5 N, and the toy experiences an acceleration of 6.25 . What is the mass of the toy?
  1. A 50.0 kg bucket is being lifted by a rope. The rope will not break if the tension is 525 N or less. The bucket started at rest, and after being lifted 3.0 m, it is moving at 3.0 m/s. If the acceleration is constant, is the rope in danger of breaking?
  1. You are helping to repair a roof by loading equipment into a bucket that workers hoist to the rooftop. If the rope is guaranteed not to break as long as the tension does not exceed 450 N and you fill the bucket until it has a mass of 42 kg, what is the greatest acceleration that the workers can give the bucket as they pull it to the roof?
  1. In the figure, A, B, and C show three situations in which one or two forces act on a puck that moves over frictionless ice along an x axis, in one-dimensional motion. The puck’s mass is m = 0.20 kg. Forces and are directed along the axis and have magnitudes and . Force is directed at angle and has a magnitude . In each situation, what is the acceleration of the puck on the horizontal axis?

(SUPER NORMAL MODE)

  1. A passenger of mass m = 72.2 kg stands on a platform scale in an elevator cab. We are concerned with the scale readings when the cab is stationary and when it is moving up or down. NOTE: The reading on the scale is equal to the magnitude of the normal force on the passenger from the scale (Newton’s 3rd Law).

(a)Find a general solution for the scale reading, whatever the vertical motion of the cab.

(b)What does the scale read if the cab is stationary?

(c)What does the scale read if the cab is moving upward at a constant rate of 0.50 m/s?

(d)What does the scale read if the cab accelerates upward at ?

(e)What does the scale read if the cab accelerates downward at ?

  1. A constant horizontal force of magnitude 20 N is applied to block A of mass , which pushes against block B of mass . The blocks slide over a frictionless surface, along an x axis.

(a)What is the acceleration of the blocks?

(b)What is the horizontal force on block B from Block A (as shown in image c)?

  1. Two horizontal forces act on a 2.0 kg chopping block that can slide over a frictionless kitchen counter, which lies in anxy plane. One force is . Find the acceleration of the chopping block in unit-vector notation when the other force is:

(a)

(b)

(c)

  1. Only two horizontal forces act on a 3.0 kg body that can move over a frictionless floor. One force is 9.0 N, acting due east, and the other is 8.0N, acting north of west. What is the magnitude of the body’s acceleration?
  1. A 2.00 kg object is subjected to three forces that give it an acceleration . If two of the three forces are and, find the third force.

(CONTINUED ON NEXT PAGE)

  1. Three astronauts, propelled by jet backpacks, push and guide a 120 kg asteroid toward a processing dock, exerting the forces shown in the figure, with .

What is the asteroid’s acceleration:

(a)In unit-vector notation?

(b)As a magnitude?

(c)A direction relative to the positive direction of the x-axis?

  1. An 11.0 kg salami is supported by a cord that runs around a pulley and to a scale. The opposite end of the scale is attached by a cord to a wall. What is the reading on the scale?

  1. In the figure below, let the mass of the block be 8.5 kg and the angle be . Find (a) the tension in the cord and (b) the normal force acting on the block. (c) If the cord is cut, find the magnitude of the resulting acceleration of the block?
  1. A “sun yacht” is a spacecraft with a large sail that is pushed by sunlight. Although such a push is tiny in everyday circumstances, it can be large enough to send the spacecraft outward from the Sun on a cost-free but slow trip. Suppose that the spacecraft has a mass of 900 kg and receives a push of 20 N.

(a)What is the magnitude of the resulting acceleration?

(b)If the craft starts from rest, how far will it travel in 1 day?

(c)How fast will it then be moving after starting from rest and traveling for 1 day?

  1. The tension at which a fishing line snaps is commonly called the line’s “strength.” What minimum strength is needed for a line that is to stop a salmon of weight 85 N in 11 cm if the fish is initially drifting at 2.8 m/s? Assume a constant deceleration.
  1. A 500 kg rocket sled can be accelerated at a constant rate from rest to 1600 km/h in 1.8 s. What is the magnitude of the required net force?
  1. A crate of mass m = 100 kg is pushed at constant speed up a frictionless ramp ( by a horizontal force . What are the magnitudes of (a) and (b) the force on the crate from the ramp?

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