Questions related to Kinematics

[alexandria]

Homework Statement

so I am sending my unit in for marking, and i collected a bunch of kinematic related questions that I've attempted to answer, but don't know if I am on the right track. Any help would be appreciated. Thanks.
1.[/B]

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Homework Equations

relevant equations are listed with each question

The Attempt at a Solution

1.
The truck traveled 14.0 km (South) in 15 min. The truck continued another 6 km at a slower pace over 10 min, and then stayed at this location for 5 min. The truck continued on at a constant speed for another 8 km towards the destination, taking 15 min for this portion of its journey.

2.
Displacement = 131 km (South)

Average velocity = total displacement / total time

Average velocity = 131 km (S) / 2.0 h

Average velocity = 65.5 km /h (south)

3.
a)

d = v x t

Time to cross river:

t = d / v

= 0.032 km / 2.5 km/h

= 0.0128 hrs

Walking distance:

d = (1.2 km/h) x (0.0128 hrs)

d = 0.01536 km = 15.36 m

Sandra will have to walk 15.36 m to reach the farmer’s market.

b)
Time it takes to cross the river:

t = d / v

t = 32.0 m (E) / 0.69 m/s (E)

t = 46 s

Time it takes to walk the riverbank:

t = d / v

t = 15.36 m / 0.72 m/s

t = 21 s

Walking to the farmer’s market will result in the shortest time for Sandra to reach her destination.

4.
Increase the launch angle above 45 degrees, to reduce the horizontal displacement. This way the water balloon will hit the target instead of passing it.

5.
is it because the supplies will be blown off course??

 

[andrewkirk]

The truck continued another 6 km at a slower pace over 10 min

Are you sure it 'continued' in the same direction? What does the fact that the North-South coordinate is reducing over this 10 minutes tell us?

The truck continued on at a constant speed for another 8 km towards the destination

Towards the destination? What do you mean by the destination? A place to deliver cabbages, or the home depot?

 

[haruspex]

Why have you reposted the first question in a new thread? You previously posted it here https://www.physicsforums.com/threads/kinematics-identifying-and-describing-types-of-motion.863163/, but failed to reply to either of the responses there. If you do not understand the responses say so, don't just repost.

 

[alexandria]

ok sorry about that :P
"Are you sure it 'continued' in the same direction? What does the fact that the North-South coordinate is reducing over this 10 minutes tell us?"
is the truck now traveling in an east-south direction?

 

[andrewkirk]

is the truck now traveling in an east-south direction?

We are given no information about its East-West coordinates. Only the North-South coordinates are given. Hence we should assume that it is traveling only along a road that runs North-South.

 

[alexandria]

so was the truck traveling North initially, but then began to travel towards the south direction?

 

[andrewkirk]

No, traveling South first, because the coordinate given is the km to the South. THen turns and travels North later.

 

[haruspex]

so was the truck traveling North initially, but then began to travel towards the south direction?

Nearly right. That might not be what you intended to say.

 

[alexandria]

so is this how it goes:
The truck traveled 14.0 km (South) in 15 min. The truck then traveled another 6 km North at a slower pace over 10 min, staying at this location for 5 min. The truck continued on at a constant speed for another 8 km towards the destination, taking 15 min for this portion of its journey.

also am i right that the truck continues at a constant speed?

 

[haruspex]

so is this how it goes:
The truck traveled 14.0 km (South) in 15 min. The truck then traveled another 6 km North at a slower pace over 10 min, staying at this location for 5 min. The truck continued on at a constant speed for another 8 km towards the destination, taking 15 min for this portion of its journey.

also am i right that the truck continues at a constant speed?

Yes, but as has already been suggested you should state the speeds.

 

[alexandria]

oh ok, but I am following the example in my lesson, so in that context do you think my answer is valid.

 

[haruspex]

oh ok, but I am following the example in my lesson, so in that context do you think my answer is valid.
View attachment 97907
View attachment 97906

If that's the example to be followed then not mentioning the actual speeds is fine.

 

[alexandria]

ok thank you for your help.