Quick Motion Question - Rejogging memory after a while.

In summary: The SUVAT equations are:-SUVAT_1: v1 = u1 + v2 t-SUVAT_2: v2 = u2 + v3 t-SUVAT_3: v3 = u3 + v4 t-SUVAT_4: v4 = u4 + v5 tWhich equation should you use?You should use SUVAT_4.
  • #1
AviationFanBoy
15
0

Homework Statement


A car traveling with a constant speed of 80km/hr passes a stationary motorcycle policeman. The policeman sets off in pursuit, accelerating uniformly to 80km/hr in 10 seconds and reaching a constant speed of 100km/hr in a further 5 secs. At what time will the policeman catch up with the car.

Homework Equations


N/A

The Attempt at a Solution


I figure if they catch up to each other, then assuming they began from the same point then their displacement will be equal to each other. Thus I did, the speeding car was doing 80km in one hour, and the cop was doing 100 km in one hour. Thus the cop would reach 80km displacement in 48 mins. (0.8 x 60 mins)
 
Physics news on Phys.org
  • #2
AviationFanBoy said:
the cop would reach 80km displacement in 48 mins.
How did you determine that 80km was the appropriate displacement?
Hint: how much lead does the motorist have when the cop first reaches 100km/h?
 
  • #3
15 secs before he reaches 100km/hr. So then what?
 
  • #4
AviationFanBoy said:
15 secs before he reaches 100km/hr. So then what?
I mean lead as a distance.
 
  • #5
haruspex said:
I mean lead as a distance.
333m. As 80km/hr = 22m/s (80/3.6) = 22m/s.
Thus, 15 secs = 333.3 (infinite) meters.
 
  • #6
AviationFanBoy said:
333m. As 80km/hr = 22m/s (80/3.6) = 22m/s.
Thus, 15 secs = 333.3 (infinite) meters.
That's how far the car goes in 15 seconds, but the cop is not standing still.
 
  • #7
haruspex said:
That's how far the car goes in 15 seconds, but the cop is not standing still.

The car has a 333m lead over the policeman. Thats what you asked?
 
  • #8
AviationFanBoy said:
The car has a 333m lead over the policeman. Thats what you asked?
333m is the lead he would have had if the policeman had not given chase. Where is the cop after 15 seconds?
 
  • #9
After 15 seconds he is traveling at 100 km/hr and has traveled 360m. As for the first 10 seconds he covers 222m as he is traveling at 80km/hr, and for the next 5 seconds he travels at 100km/hr covering 138m thus after 15 secs the cop is 360meters from the starting position.
 
  • #10
AviationFanBoy said:
As for the first 10 seconds he covers 222m as he is traveling at 80km/hr.
No he isn't - read the question again.
 
  • #11
Sorry, he covers 416 meters in the 15 seconds. As 100/3.6 = 27.8 x15 = ~416m.
 
  • #12
AviationFanBoy said:
Sorry, he covers 416 meters in the 15 seconds. As 100/3.6 = 27.8 x15 = ~416m.
Pay attention! The cop is not moving at uniform speed. For the first 10 seconds he accelerates uniformly from 0 to 80km/h. Do you know the SUVAT equations? These can be used for uniform (i.e. constant) acceleration.
 
  • #13
Yes, i know them. How are they linked though. I reliaze he accelerates at different rates from 0 to 10 then 10 to 15 seconds. Hence why I said, After 15 seconds he is traveling at 100 km/hr and has traveled 360m. As for the first 10 seconds he covers 222m as he is traveling at 80km/hr, and for the next 5 seconds he travels at 100km/hr covering 138m thus after 15 secs the cop is 360meters from the starting position.
 
  • #14
AviationFanBoy said:
As for the first 10 seconds he covers 222m as he is traveling at 80km/hr
No he isn't! Why do you keep asserting that when I have already pointed out that it is wrong?
He starts at 0 km/h, and only reaches 80km/h at the end of the 10 seconds. He does not travel at 80km/h for 10 seconds.
In the usual form, there are five SUVAT equations, each involving four variables. Typically, you know the value of three, and you want to find a fourth, so pick the equation that involves those four variables.
What three values do you know here? What other variable do you want to determine? Which equation should you use?
 

FAQ: Quick Motion Question - Rejogging memory after a while.

1. What is Quick Motion Question?

Quick Motion Question is a method used to quickly jog one's memory after a period of time has passed. It involves asking a series of rapid-fire questions to stimulate the brain and help recall information.

2. How does Quick Motion Question work?

Quick Motion Question works by activating the brain's neural pathways and connections. By asking rapid-fire questions, it forces the brain to quickly process and retrieve information, which can improve memory recall.

3. When should Quick Motion Question be used?

Quick Motion Question can be used in any situation where one needs to quickly recall information after a period of time has passed. It is particularly useful for studying, preparing for exams, or remembering important details for a presentation or meeting.

4. Are there any potential downsides to using Quick Motion Question?

While Quick Motion Question can be an effective memory recall technique, it may not work for everyone. Some people may find the rapid-fire questioning overwhelming, which can hinder memory recall. It is important to use this method in moderation and find what works best for each individual.

5. Are there any other memory recall techniques that work well with Quick Motion Question?

Yes, there are several memory recall techniques that can work well with Quick Motion Question. Some examples include visualization, mnemonic devices, and chunking information into smaller, more manageable pieces. It is important to experiment and find which techniques work best for each individual.

Back
Top