The -2.1s simply comes from the fact that it's a parabola (a quadratic equation) and this means that we will have two solutions, in this example we sort of ignored the left side of the parabola and only focused on the positive solution (when the ball hits the ground/x-axis) which took 4.21 seconds, but you can imagine if the ball was thrown in the complete opposite direction, then it would've taken 2.1 seconds for it to hit the ground which makes sense from the illustration, the negative sign comes from the fact that it's the opposite (just like when you multiply a vector by -1, it points in the opposite direction with the same magnitude).
4:01 couldnt you just solve for Vf (by using Vf^2=Vi^2+2aX) but this time with angles in the y direction (because we know the most about y), and then rearrange the equation Vf=Vi+at to t=(Vf-Vi)/a to find the time?
But the time period we are finding here is not the timeperiod till which the ball stayed in the air,it is calculated using displcement right????,please correct me dr.A
emily ballard, Great question. I'll have to make another video. Thanks for the comment, and keep up with the physics! You might also like my new website: www.universityphysics.education Cheers, Dr. A
When you were mentally trying to figure out the value of sin30, I heard you mentioning sines 60 and 90. Is there a way to mentally check their own values too without a calculator. Is there some sort of formula or technique
Danny Bangs, Thanks for the comment, and keep up with the physics! Yes, we know that a 30-60-90 triangle is a 1-sqrt3-2 triangle. So sin30 = 1/2, cos30 = sqrt3/2. Rotate to 60 and you get sin60=sqrt3/2 and cos60=1/2. Hope this helps. You might also like my new website: www.universityphysics.education Cheers, Dr. A
A good idea is to memorise the unit circle, it has coordinates (cos, sin) just like (x, y). All you need to remember is that each quadrant has 3 angles, so 30, 45, 60 then 90, 120, 135, 150 and then 180 and so on... the values for each angle (cos first) goes as follows... sqrt(3)/2 -> sqrt(2)/2 -> 1/2 and opposite for sin which is 1/2 -> sqrt(2)/2 -> sqrt(3)/2. So the only thing I remember is cos(30) and then I can derive every other angle for cos or sin from there, just remember the sign depending on which quadrant we're in and that's about it.
Hello professor.. My name is Arjun .. I had a doubt .. Two ball are projected at different angles from the same place and with same initial speed of 50 m/s. Both ball have Same rage of 216m . The difference in their time of flight is close to ?... sir please help me ...?
If they have the same range, then they were shot at 45˚ ± Δ. For example, a projectile at 60˚ and 30˚ have the same range. Same with 75˚ and 15˚. Once you know the angle, you can calculate the vertical component of velocity which will tell you how long each was in the air. You probably know that the one that goes at a steeper angle (more vertical) will be in the air longer. Good luck, Dr. A
he drew normally and simply mirrored the video. Note the buttons on his shirt and pocket--they are on the wrong side. also he is drawing left handed but odds are far higher is right handed. also note the ring is on the wrong hand.
Hi Sir can you help me with my homework Question 1. A 35 g bullet was fired horizontally from a gun with a velocity of 320.0 m/s. If the barrel is 1.1 meter from the ground, how long will it take for the bullet to reach the ground? (ROUND YOUR ANSWER TO 1 DECIMAL PLACE, Ex. 100.0) Question 2 . A 35 g bullet was fired horizontally from a gun with a velocity of 315.0 m/s. If the barrel is 1.5 meter from the ground, how far will the bullet reach as it first hit the ground? (ROUND YOUR ANSWER TO 1 DECIMAL PLACE, Ex. 100.0) THank you so much
I can't chew gum and walk at the same time. He's writing, left-handed, backwards, and explaining physics so clearly. Well done professor. Subscribing.
Welcome aboard.
Not writing backwards, though. Mirror image.
Cheers,
Dr. A
@@yoprofmatt Ah, The Learning Glass, excellent tool!
Holy moly
I have watched every video of your playlist. I am in highschool and it helped me a lot. Thanks Dr A.👍💚
Great job Professor, Thank you.
Thank u so much! Great job professor! Just subscribed!
thank you prof. all love from south africa🙏
The -2.1s simply comes from the fact that it's a parabola (a quadratic equation) and this means that we will have two solutions, in this example we sort of ignored the left side of the parabola and only focused on the positive solution (when the ball hits the ground/x-axis) which took 4.21 seconds, but you can imagine if the ball was thrown in the complete opposite direction, then it would've taken 2.1 seconds for it to hit the ground which makes sense from the illustration, the negative sign comes from the fact that it's the opposite (just like when you multiply a vector by -1, it points in the opposite direction with the same magnitude).
Excellent discussion.
Cheers,
Dr. A
Fascinating interpretation of that neg time solution!
fizixx,
Thanks for the comment, and keep up with the physics!
You might also like my new website: www.universityphysics.education
Cheers,
Dr. A
@@yoprofmatt Thanks :)
I don't understand the negative time part...
4:01 couldnt you just solve for Vf (by using Vf^2=Vi^2+2aX) but this time with angles in the y direction (because we know the most about y), and then rearrange the equation Vf=Vi+at to t=(Vf-Vi)/a to find the time?
How to find at what angle will it hit the ground?
But the time period we are finding here is not the timeperiod till which the ball stayed in the air,it is calculated using displcement right????,please correct me dr.A
What was the time it took from the apex to the ground though?
emily ballard,
Great question. I'll have to make another video.
Thanks for the comment, and keep up with the physics!
You might also like my new website: www.universityphysics.education
Cheers,
Dr. A
Thanks Prof.
When you were mentally trying to figure out the value of sin30, I heard you mentioning sines 60 and 90. Is there a way to mentally check their own values too without a calculator. Is there some sort of formula or technique
Danny Bangs,
Thanks for the comment, and keep up with the physics!
Yes, we know that a 30-60-90 triangle is a 1-sqrt3-2 triangle. So sin30 = 1/2, cos30 = sqrt3/2. Rotate to 60 and you get sin60=sqrt3/2 and cos60=1/2. Hope this helps.
You might also like my new website: www.universityphysics.education
Cheers,
Dr. A
A good idea is to memorise the unit circle, it has coordinates (cos, sin) just like (x, y). All you need to remember is that each quadrant has 3 angles, so 30, 45, 60 then 90, 120, 135, 150 and then 180 and so on... the values for each angle (cos first) goes as follows... sqrt(3)/2 -> sqrt(2)/2 -> 1/2 and opposite for sin which is 1/2 -> sqrt(2)/2 -> sqrt(3)/2. So the only thing I remember is cos(30) and then I can derive every other angle for cos or sin from there, just remember the sign depending on which quadrant we're in and that's about it.
Hello professor.. My name is Arjun .. I had a doubt .. Two ball are projected at different angles from the same place and with same initial speed of 50 m/s. Both ball have Same rage of 216m . The difference in their time of flight is close to ?... sir please help me ...?
If they have the same range, then they were shot at 45˚ ± Δ. For example, a projectile at 60˚ and 30˚ have the same range. Same with 75˚ and 15˚. Once you know the angle, you can calculate the vertical component of velocity which will tell you how long each was in the air. You probably know that the one that goes at a steeper angle (more vertical) will be in the air longer.
Good luck,
Dr. A
First of all I am soo thankful for taking your precious time for clearing my doubt.... Thank you soo much professor. .Thank you..
Thank you for the comment. Keep up with the physics.
Cheers,
Dr. A
he drew normally and simply mirrored the video. Note the buttons on his shirt and pocket--they are on the wrong side. also he is drawing left handed but odds are far higher is right handed. also note the ring is on the wrong hand.
Correct. Secrets revealed here:
ruclips.net/video/CWHMtSNKxYA/видео.html
Cheers,
Dr. A
At marker 3:05 you multiply by two "just for kicks".. is that just to get rid of the 1/2 and make the equation more simple to solve?
Yep. I don't like stuff in the denominator before using the quadratic formula.
Cheers,
Dr. A
Hi Sir can you help me with my homework
Question 1. A 35 g bullet was fired horizontally from a gun with a velocity of 320.0 m/s. If the barrel is 1.1 meter from the ground, how long will it take for the bullet to reach the ground? (ROUND YOUR ANSWER TO 1 DECIMAL PLACE, Ex. 100.0)
Question 2 . A 35 g bullet was fired horizontally from a gun with a velocity of 315.0 m/s. If the barrel is 1.5 meter from the ground, how far will the bullet reach as it first hit the ground? (ROUND YOUR ANSWER TO 1 DECIMAL PLACE, Ex. 100.0)
THank you so much