Calculate Initial Velocity of Boat Moving 15 km

[ArcherofScience]

Homework Statement

A boat moves 15 km as it accelerates at 3.5 m/s^2 for 1.5 minutes. What is the truck's initial velocity?

Homework Equations

i'm stuck on what formula to use...

3. The Attempt at a Solution [/]
vf^2=vo^2+2ax? ...

 

[Simon Bridge]

Homework Statement

A boat moves 15 km as it accelerates at 3.5 m/s^2 for 1.5 minutes. What is the truck's initial velocity?

What does the truck have to do with the boat?

i'm stuck on what formula to use...

3. The Attempt at a Solution [/]
vf^2=vo^2+2ax? ...

If you are stuck on a formula, draw the v-t diagram.
The boat starts at some speed u at t=0 and increases it's speed to speed v at t=90s.
This gives you a trapezium shape with two unknown points in it.

The slope of the line is the acceleration - which you have been given.
The area under the graph is the distance - which you have been given.
The rest is basic geometry.

(The other approach is to list all the kinematic equations, and list the variables you know. The equation with all the ones you know and the one you want to find is the correct one.)

 

[chief10]

You will have to employ your elementary equations of motion in Physics. This question is quite basic. I'm guessing the truck and the boat are the same thing and you just mixed them up.
The SUVAT equation you used is incorrect because you are not given your final velocity so employing v^2=u^2+2as is not helpful because you're just introducing more unknown variables.

Below is the correct method of solving this question if you don't want to sketch a graph. Although it's good to know how to do them.

s (displacement) =15km=15000m
a (acceleration) =3.5
t (time) =1.5mins=90
u (initial velocity)=?

s = u*t+(0.5)at^2have a go at that, that should do it.

 

[Simon Bridge]

The suvat method is focussed around the discipline of laying out the variables and choosing the equation. The bit where the numbers go into the equation is just a formality when you think about it.

Giving someone the specific equation to use, therefore, removes the skill part of the problem as well as all the physics and turns the experience into a mindless algorithm -- all without actually solving the problem of how to choose the right equation. You may as well program a suvat app on a phone! Thus the student is unlikely to learn how and will need the same help next time.

It is a point in pedagogy that people who have trouble with one method will benefit from learning another.

eg. Those with trouble figuring the suvat equation to use often do better geometrically ... if they can get past the common fear of sketching graphs.

 

[Nickie]

I'm still not sure what to do with the given time and distance values.

I would first identify the known values and the unknown value in the given problem. The known values are the distance (15 km) and the acceleration (3.5 m/s^2), while the unknown value is the initial velocity of the boat.

To solve this problem, we can use the formula v = u + at, where v is the final velocity, u is the initial velocity, a is the acceleration, and t is the time.

Since we are given the distance in kilometers and the acceleration in meters per second squared, we need to convert these values to a consistent unit. Let's convert the distance from kilometers to meters by multiplying it by 1000, giving us a distance of 15,000 meters.

Now, we can plug in the known values into the formula:

v = u + at
15,000 = u + (3.5)(1.5*60)
15,000 = u + 315

To solve for u, we need to isolate it on one side of the equation by subtracting 315 from both sides:

15,000 - 315 = u
14,685 = u

Therefore, the initial velocity of the boat is 14,685 m/s.

It's important to note that the given time of 1.5 minutes was converted to seconds by multiplying it by 60, as time is typically expressed in seconds when using formulas involving acceleration. Also, the formula used was the basic formula for motion with constant acceleration, which is often used to solve problems involving motion and displacement.