Does A Car Headrest Help To Guard Against Whiplash In A Rear-End Collision?
14. In terms of Newton’s fist law, how does a car headrest help to guard against whiplash in a rear end collision?
In a rear-end collision, your body moves forward with the car, your head is at rest and tends to stay at rest. Relative to your body, which means it is jerking back. The headrest brings your head along with the rest of the body.
18. Each bone in the chain of bones forming your spine is separated from its neighbors by disks of elastic tissue. What happens, then, when you jump heavily onto your feet from an elevated position? Can you think of a reason why you are a little taller in the morning than at night?
Each of the elastic tissue tends to compress to each other because of newton’s first law.
23. Can an object be in …show more content…
mechanical equilibrium when only a single force acts on it? Explain.
If the net force on the object is zero, we say that something is in mechanical equilibrium.
27. Nellie Newton hangs at rest from the ends of the rope as shown. How does the reading on the scale compare with her weight?
The scale will read half of her weight.
29. For the pulley system shown, what is the upper limit of weight the strong man can life?
Any weight that under his weight.
38. If you pull horizontally on a crate with a force of 200 N, it slides across the floor in dynamic equilibrium. How much friction is acting on the crate?
200 N since it is neither accelerating nor decelerating. The New force is 0.
46. If you toss a coin straight upward while riding in a train, where does the coin land when the motion of the train is uniform along a straight-line track? When the train slows while the coin is in the air? When the train is turning?
The coin has the same forward speed as the train. If the train’s speed is uniform, the coin will drop straight back into your hand. If the train slows while the coin is in the air, the coin will have a greater forward speed than the train and so will move some distance forward. It will drop in front of you. If the train is turning, the coin will continue along a tangent to the curve, while the train pulls inwards around the curve. The coin will appear to move outwards, away from the curve.
Problem 1.
Lucy Lightfoot stands with one foot on one bathroom scale and her other foot on a second bather scales. Each scale reads 350 N. what is Lucy’s weight?
350 X2= 700 N
Problem 3
The sketch shows a painter’s scaffold in mechanical equilibrium. The person in the middle weights 500N, and the tensions in each rope are 400N. What is the weight of the scaffold?
(400N X2 ) – 500N = 300N
Problem 4
A different scaffold that weights 400N supports 2 printers, one 500N and the other 400N. The reading in the left scale is 800N. What is the reading in the right hand scale?
500N + 800N – 800N = 500N
Chapter 3
4. One airplane travels due north at 300km/h while another travels due south at 300 km/h. Are their speeds the same? Are their velocities the same? Explain.
They have the same speed, but different velocities. Velocity is a vector, including speed and direction. They have opposite directions, therefore cannot have the same velocity.
13.
Starting from rest, one car accelerates to a speed of 50km/h, and another car accelerates to a speed of 60km/h. Can you say which car underwent the greater acceleration? Why or why not?
We cannot tell which car underwent the greater acceleration without knowing the time.
30. Someone standing at the edge of a cliff throws a ball nearly straight up at a certain speed and another ball nearly straight up at a certain speed and another ball nearly straight down with the same initial speed. If air resistance is negligible, which ball will have the greater speed when it strikes the ground below?
Both balls strike the ground with the same speed. The ball thrown upwards has the same initial speed as the one thrown downwards.
35. Consider a vertically launched projectile when air drag is negligible. When is the acceleration due to gravity greater? When ascending, at the top, or when descending? Defend your answer.
The acceleration due to gravity remains a constant g at all points along its path as long as no other forces like air drag act on the projectile.
36. Extend tables 3.2 and 3.3 to include times of fall of 6 to 10 s assuming no air resistance time of fall (seconds)
Velocity acquired (Meters/ second) 0
0
1
10
2
20
3
30
4
40
5
50
6
60
7
70
8
80
9
90
10
100 time of fall (seconds)
Distance Fallen (meters)
0
0
1
5
2
20
3
45
4
80
5
125
6
180
7
245
8
320
9
405
10
500
1. You toss a ball straight up with an initial speed of 30m/s. how high does it go, and how long is it in the air?
Since it starts going up at 30 m/s and loses 10m/s each second. Its time going up is 3 seconds. Its time falling down is 3 seconds as well. 3x2 = 6 seconds.
Distance = ½ gt^2 = 10 /2 X 3^2 = 5 X 9 = 45m.
2. A ball is tossed with enough speed straight up so that it is in the air several seconds.
a) what is the velocity of the ball when it reaches its highest point?
0. It is in rest position at the highest point.
b) what is its velocity 1s before it reaches its highest point?
9.8 m/s
c) what is the change in its velocity during this 1-s interval? from 9.8/s up to 0m/s
d) what is its velocity 1s after it reaches its highest point? from 0m/s to 9.8m/s down
e) what is the change in velocity during this 1-s interval?
0m/s to 9.8m/s down
f) what is the change in velocity during the 2-s interval?
9.8m/s X 2 = 19.6m/s
g) what is the acceleration of the ball during any of these time intervals and at the moment the ball has zero velocity? a = 9.8 m/s^2 down
3. What is the instantaneous velocity of a freely falling object 10s after it is released from a position of rest? What is its average velocity during this 10-s interval? How far will it fall during this time?
4. A car takes 10s to go from v=0m/s to v=25 at constant acceleration. If you wish to find the distance traveled using the equation d = ½ at^2, what value should you use for a?
5. Surprisingly, very few athletes can jump more than 2 feet (0.6m) straight up. Use d = 1/2gt^2 and solve for the time one spends moving upward in a 0.6 m vertical jump. Then double it for the “hang time” – the time one’s feet are off the ground.
Chapter 4
5. Since an object weights less on the surface of the Moon than on Earth’s surface, does it have less inertia on the Moon’s surface?
No, inertia involves mass, not weight.
10. Your empty hand is not hurt when it bangs lightly against a wall. Why does it hurt if you’re carrying a heavy load? Which of Newton’s laws is most applicable here?
1st Law, the heavier object wants to keep moving through your hand, but obviously your hand gets in the ways.
16. what weight change occurs when your mass increases by 2 kg?
If it happens to be on the earth, it becomes 19.6 N heavier.
22. The auto in the sketch moves forward as the brakes are applied. A bystander says that during the interval of braking, the auto’s velocity and acceleration are in opposite directions. Do you agree or disagree?
No, I disagree. The auto’s velocity and acceleration can be in opposite directions unless the auto is backed up. The auto was just stopping. The velocity and acceleration would decrease only.
26. Three identical blocks are pulled, as shown, on a horizontal frictionless surface. If tension in the rope held by the hand is 30N, what is the tension in the other ropes?
31 sketch the path of a ball tossed vertically into the air. Draw the ball halfway to the top, at the top, and halfway down to its starting point. Draw a force vector on the ball in all three positions. Is the vector the same or different in the three locations? Is the acceleration the same or different in the 3 position?
54 why is it that a cat that accidentally falls from the top of a 50-story building hits a safety net below no faster than if it fell from the twentieth story?
In a rear-end collision, your body moves forward with the car, your head is at rest and tends to stay at rest. Relative to your body, which means it is jerking back. The headrest brings your head along with the rest of the body.
18. Each bone in the chain of bones forming your spine is separated from its neighbors by disks of elastic tissue. What happens, then, when you jump heavily onto your feet from an elevated position? Can you think of a reason why you are a little taller in the morning than at night?
Each of the elastic tissue tends to compress to each other because of newton’s first law.
23. Can an object be in …show more content…
mechanical equilibrium when only a single force acts on it? Explain.
If the net force on the object is zero, we say that something is in mechanical equilibrium.
27. Nellie Newton hangs at rest from the ends of the rope as shown. How does the reading on the scale compare with her weight?
The scale will read half of her weight.
29. For the pulley system shown, what is the upper limit of weight the strong man can life?
Any weight that under his weight.
38. If you pull horizontally on a crate with a force of 200 N, it slides across the floor in dynamic equilibrium. How much friction is acting on the crate?
200 N since it is neither accelerating nor decelerating. The New force is 0.
46. If you toss a coin straight upward while riding in a train, where does the coin land when the motion of the train is uniform along a straight-line track? When the train slows while the coin is in the air? When the train is turning?
The coin has the same forward speed as the train. If the train’s speed is uniform, the coin will drop straight back into your hand. If the train slows while the coin is in the air, the coin will have a greater forward speed than the train and so will move some distance forward. It will drop in front of you. If the train is turning, the coin will continue along a tangent to the curve, while the train pulls inwards around the curve. The coin will appear to move outwards, away from the curve.
Problem 1.
Lucy Lightfoot stands with one foot on one bathroom scale and her other foot on a second bather scales. Each scale reads 350 N. what is Lucy’s weight?
350 X2= 700 N
Problem 3
The sketch shows a painter’s scaffold in mechanical equilibrium. The person in the middle weights 500N, and the tensions in each rope are 400N. What is the weight of the scaffold?
(400N X2 ) – 500N = 300N
Problem 4
A different scaffold that weights 400N supports 2 printers, one 500N and the other 400N. The reading in the left scale is 800N. What is the reading in the right hand scale?
500N + 800N – 800N = 500N
Chapter 3
4. One airplane travels due north at 300km/h while another travels due south at 300 km/h. Are their speeds the same? Are their velocities the same? Explain.
They have the same speed, but different velocities. Velocity is a vector, including speed and direction. They have opposite directions, therefore cannot have the same velocity.
13.
Starting from rest, one car accelerates to a speed of 50km/h, and another car accelerates to a speed of 60km/h. Can you say which car underwent the greater acceleration? Why or why not?
We cannot tell which car underwent the greater acceleration without knowing the time.
30. Someone standing at the edge of a cliff throws a ball nearly straight up at a certain speed and another ball nearly straight up at a certain speed and another ball nearly straight down with the same initial speed. If air resistance is negligible, which ball will have the greater speed when it strikes the ground below?
Both balls strike the ground with the same speed. The ball thrown upwards has the same initial speed as the one thrown downwards.
35. Consider a vertically launched projectile when air drag is negligible. When is the acceleration due to gravity greater? When ascending, at the top, or when descending? Defend your answer.
The acceleration due to gravity remains a constant g at all points along its path as long as no other forces like air drag act on the projectile.
36. Extend tables 3.2 and 3.3 to include times of fall of 6 to 10 s assuming no air resistance time of fall (seconds)
Velocity acquired (Meters/ second) 0
0
1
10
2
20
3
30
4
40
5
50
6
60
7
70
8
80
9
90
10
100 time of fall (seconds)
Distance Fallen (meters)
0
0
1
5
2
20
3
45
4
80
5
125
6
180
7
245
8
320
9
405
10
500
1. You toss a ball straight up with an initial speed of 30m/s. how high does it go, and how long is it in the air?
Since it starts going up at 30 m/s and loses 10m/s each second. Its time going up is 3 seconds. Its time falling down is 3 seconds as well. 3x2 = 6 seconds.
Distance = ½ gt^2 = 10 /2 X 3^2 = 5 X 9 = 45m.
2. A ball is tossed with enough speed straight up so that it is in the air several seconds.
a) what is the velocity of the ball when it reaches its highest point?
0. It is in rest position at the highest point.
b) what is its velocity 1s before it reaches its highest point?
9.8 m/s
c) what is the change in its velocity during this 1-s interval? from 9.8/s up to 0m/s
d) what is its velocity 1s after it reaches its highest point? from 0m/s to 9.8m/s down
e) what is the change in velocity during this 1-s interval?
0m/s to 9.8m/s down
f) what is the change in velocity during the 2-s interval?
9.8m/s X 2 = 19.6m/s
g) what is the acceleration of the ball during any of these time intervals and at the moment the ball has zero velocity? a = 9.8 m/s^2 down
3. What is the instantaneous velocity of a freely falling object 10s after it is released from a position of rest? What is its average velocity during this 10-s interval? How far will it fall during this time?
4. A car takes 10s to go from v=0m/s to v=25 at constant acceleration. If you wish to find the distance traveled using the equation d = ½ at^2, what value should you use for a?
5. Surprisingly, very few athletes can jump more than 2 feet (0.6m) straight up. Use d = 1/2gt^2 and solve for the time one spends moving upward in a 0.6 m vertical jump. Then double it for the “hang time” – the time one’s feet are off the ground.
Chapter 4
5. Since an object weights less on the surface of the Moon than on Earth’s surface, does it have less inertia on the Moon’s surface?
No, inertia involves mass, not weight.
10. Your empty hand is not hurt when it bangs lightly against a wall. Why does it hurt if you’re carrying a heavy load? Which of Newton’s laws is most applicable here?
1st Law, the heavier object wants to keep moving through your hand, but obviously your hand gets in the ways.
16. what weight change occurs when your mass increases by 2 kg?
If it happens to be on the earth, it becomes 19.6 N heavier.
22. The auto in the sketch moves forward as the brakes are applied. A bystander says that during the interval of braking, the auto’s velocity and acceleration are in opposite directions. Do you agree or disagree?
No, I disagree. The auto’s velocity and acceleration can be in opposite directions unless the auto is backed up. The auto was just stopping. The velocity and acceleration would decrease only.
26. Three identical blocks are pulled, as shown, on a horizontal frictionless surface. If tension in the rope held by the hand is 30N, what is the tension in the other ropes?
31 sketch the path of a ball tossed vertically into the air. Draw the ball halfway to the top, at the top, and halfway down to its starting point. Draw a force vector on the ball in all three positions. Is the vector the same or different in the three locations? Is the acceleration the same or different in the 3 position?
54 why is it that a cat that accidentally falls from the top of a 50-story building hits a safety net below no faster than if it fell from the twentieth story?