Definitions: Newton’s 3rd Law Vector Components (what do they tell us?) Vector N

Question

Definitions:

Newton’s 3rd Law
Vector Components (what do they tell us?)
Vector
Normal Force
Momentum
Impulse
Conserved (What does this mean to a physicist?)
Law of Conservation of Momentum
Elastic vs. Inelastic Collision

Chapter 5

28) If you stand next to a wall on a frictionless skateboard and push the wall with a force of 40N, how hard does the wall push on you? If your mass is 80kg, show that your acceleration is 0.5m/s2.

32) Each of these boxes is pulled by the same force F to the left. All the boxes have the same mass and slide on a friction-free surface. Rank the following from greatest to least (see Figure on pg 87).

a) The acceleration of the boxes.
b) The tensions in the ropes connected to the single boxes to the right in B and in C.

42) Within a book on a table, there are billions of forces pushing and pulling on all the molecules. Why is it that these forces never by chance add up to a net force in one direction, causing the book to accelerate “spontaneously” across the table?

48) You push a heavy car by hand. The car, in turn, pushes back with an opposite but equal force on you. Doesn’t this mean that the forces cancel each other, making acceleration impossible? Why or why not?

63) A stone is being accelerated vertically upward (see Figure on pg 88).

a) Draw force vectors to some suitable scale showing relative forces acting on the stone.
b) Which is the longer vector, and why?

67) A stone is at rest, interacting with both the surface of the incline and the block (see Figure on pg 89).

a) Identify all the forces that act on the stone, and draw appropriate force vectors.
b) Show that the net force on the stone is zero.

Hint: There are two normal forces on the stone.

Hint 2: Be sure the vectors you draw are for forces that act on the stone, not by the stone on the surfaces.

Note: If you are having trouble with these kind of problems (63&67), you may want to work through 62-66 as well. They are similar, and very useful practice! (Note: if a question is put on the quiz, it will be most similar to 63 or 67)

Chapter 6

13) Is it correct to say that, if no net impulse is exerted on a system, then no change in the momentum of the system will occur?

26) What is the impulse on an 8-kg ball rolling at 2m/s when it bumps into a pillow and stops?

30) Joanne drives her car with a mass of 1000kg at a speed of 20m/s. Show that to bring her car to a halt in 10s, road friction must exert a force of 2000N on the car. (Hint: You must first calculate the change in momentum and then relate that value to impulse)

34) A railroad diesel engine weighs four times as much as a freight car. If the diesel engine coasts at 5 km/hr into a freight car initially at rest, show that the speed of the coupled engine and car is 4 km/hr. Hint: You may need to use a variable for the masses here! Say the freight train has a mass of ‘m’, and the diesel engine has a mass of ‘4m’. This will make the math much easier!

45) In terms of impulse and momentum, why do air bags in cars reduce the risk of injury in accidents?

48) Why would it be a dangerous mistake for a bungee jumper to use a steel cable instead of an elastic cord?

66) How can a fully dressed person at rest in the middle of a pond on perfectly frictionless ice get to shore?

81) A 0.5-kg on an air track moves 1.0m/s to the right, heading toward a 0.8-kg cart moving to the left at 1.2m/s. What is the direction of the two-cart system’s momentum? Set up the math! You can do it!

100) Suppose that there are three astronauts outside a spaceship and they decide to play catch. All the astronauts weigh the same on Earth and are equally strong. The first astronaut throws the second one toward the third one and the game begins. Describe the motion of the astronauts as the game proceeds. How long will the game last?

Explanation / Answer

According to the chegg guidelines I am allowed to answer only 1 question at a time.

28) If you stand next to a wall on a frictionless skateboard and push the wall with a force of 40N, how hard does the wall push on you? If your mass is 80kg, show that your acceleration is 0.5m/s2.

ANSWER) Force = 40 N M = 80 kg

acceleration = Force / mass = 40 N / 80 kg = 0.500 m/s^2 =====================ANSWER)

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