Average velocity just simply be the average speed

[J-Girl]

Hi peeps, i just started intro physics but finding it sort of difficult, and attempting to do some questions but just not quite sure if I am doing it right. would so appreciate any kind of help, my teacher doesn't seem to break it down enough for me lol. can somebody just check my work, and let me know if I am right or wrong
1)A car is driven 40km at 30km/h. it then continues in the same direction for another 40km at 60km/h. what is the average velocity of the car during this 80 km trip?
In this question, would the average velocity just simply be the average speed, as its just going in one positive direction? As the 80 km took 120 minutes all up, it is just displacement/time, and the answer is 40km/h?

2) average velocity of these two cases:
a) you walk 73.2m at a speed of 1.22m/s, and then run 73.2m, at a speed of 3.05m/s along a straight track.
73.2/1.22=60m/s
73.2/3.05=24m/s
60+24/2= 42m/s= average velocity


b)You walk for 1minute at a speed of 1.22m/s, and then run for 1minute at 3.05m/s
60 x 1.22= 73.2m
60 x 3.05=183m
73.2+183=256.2-total displacement
120 seconds=total time
so 256.2/120=2.135m/s = average velocity

please let me know if I am right, id really appreciate some help:), i know theyre easy questions but I am not very confident with physics at all!:(

 

[Doc Al]

1)A car is driven 40km at 30km/h. it then continues in the same direction for another 40km at 60km/h. what is the average velocity of the car during this 80 km trip?
In this question, would the average velocity just simply be the average speed, as its just going in one positive direction? As the 80 km took 120 minutes all up, it is just displacement/time, and the answer is 40km/h?

Good!

2) average velocity of these two cases:
a) you walk 73.2m at a speed of 1.22m/s, and then run 73.2m, at a speed of 3.05m/s along a straight track.
73.2/1.22=60m/s
73.2/3.05=24m/s
60+24/2= 42m/s= average velocity

Redo this one. You're mixing up speed and time. Solve it just like the others: total displacement over total time.

b)You walk for 1minute at a speed of 1.22m/s, and then run for 1minute at 3.05m/s
60 x 1.22= 73.2m
60 x 3.05=183m
73.2+183=256.2-total displacement
120 seconds=total time
so 256.2/120=2.135m/s = average velocity

Good!

 

[J-Girl]

ohh i see, yeah that's definitely not right:) thanks for pointing it out. so total time is 73.2/1.22m/s= 60 sec
73.2/3.05m/s=24 seconds
total distance = 73.2 x 2=146.4m
velocity is 146.4/84=1.743m/s..hope that's right! thankyou for your input it really helps:)

 

[Doc Al]

so total time is 73.2/1.22m/s= 60 sec
73.2/3.05m/s=24 seconds
total distance = 73.2 x 2=146.4m
velocity is 146.4/84=1.743m/s..hope that's right!

Now you've got it.

 

[rwisz]

Hi there! It's great that you are trying to understand and work on your physics questions. To answer your first question, yes, the average velocity in this case would simply be the average speed. This is because the car is moving in one direction and there is no change in direction or acceleration involved. So, the average velocity would be 40km/120 minutes = 1/3 km/minute = 40km/h.

For the second question, your calculations and understanding seem to be correct. In both cases, the average velocity is simply the total displacement divided by the total time taken. Keep practicing and seeking help when needed, and you will definitely get more confident in physics. Good luck!