Question

A sled is pushed along an ice covered lake. It has some initial velocity before coming to a rest in 15 m. It took 23 seconds before the sled and rider come to a rest. If the rider and sled have a combined mass of 52.5 kg, what is the magnitude (amount) and direction of stopping force?

OK, so I have no idea what to do tbh. HELP PLEASE

Answer 1

@pooja195 ?

Answer 2

The most difficult part for me is the initial velocity. I don't know what it is. I don't know how to find it.

Answer 3

\[\huge~\rm~u=v-at\]
u = Initial velocity,
v = Final Velocity,
t = time taken,
a = acceleration.
This is the formula for intial velocity but in order to solve this we need the other info...

Answer 4

final velocity is 0. time taken is 23 minutes. acceleration is idk. but it is negative

Answer 5

Wouldn't it be -15?

Answer 6

but it took 23 minutes right?

Answer 7

Its decelerating...
It has some initial velocity before `coming to a rest in 15 m`.

Answer 8

Im not sure :/

Answer 9

m = meters

Answer 10

you can work this from the equations of motion
do you know them?

Answer 11

http://www.cliffsnotes.com/~/media/387da48a5492469fb38fd6dfeb115d4e.ashx?la=en

we don't know the acceleration, so you use the equation with an X in the acceleration "a" column

that is equation 2 which says

\[\Large d=\frac{1}{2}(v_0+v_f)*t\]


d = 15 meters
V0 = unknown (but can be solved for)
Vf = 0 meters per second
t = 23 seconds

Answer 12

yes. I know acceleration, which idk if i can write on here directly, f = ma, and v = d/t and magnitude is an arrow, and i need the # and the direction is the opposite i think.

Answer 13

jt has it !

Answer 14

so 15 = 1/2 ^ ( [unknown] + 0) ^ 23?

Answer 15

Once you know V0, you can find the acceleration

Then you'll use the acceleration to compute F in `F = m*a` to find the stopping force (aka frictional force)

Answer 16

I think it is 1.3 m/s because i divided 15 by 2, and then by 23 and got 1.3. Is that right?

Answer 17

so it is 0-1.3 / 23-0?

Answer 18

no that doesnt sound right

Answer 19

why not? you're using

\[\Large a = \frac{\Delta v}{\Delta t}\]

which is correct

Answer 20

but @pooja195 got the answer, and it was like 2.8 N

Answer 21

you should find that

\[\Large a = \frac{\Delta v}{\Delta t} \]
\[\Large a = \frac{v_f-v_0}{\Delta t}\]
\[\Large a = \frac{0-1.304347826}{23}\]
\[\Large a = -0.05671077504\]

So,

F = m*a
F = 52.5*(-0.05671077504)
F = -2.9773156896

Answer 22

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Answer 23

The magnitude is simply the absolute value of the force
The direction of the stopping force is the complete opposite of the motion of the sled

Answer 24

so like
------>
-2.97 N

The direction is because it is negative.

Answer 25

`but @pooja195 got the answer, and it was like 2.8 N`
I'm guessing @pooja195 rounded somewhere to get 2.8

Answer 26

I don't know what you mean by that arrow. It doesn't say which direction this sled is moving (left or right)

Answer 27

So technically, it is right, and wrong?

Answer 28

If the sled is moving left, then the stopping force is pointing to the right
If the sled is moving right, then the stopping force is pointing to the left

Answer 29

I would just say the stopping force is opposite the direction of motion (until you can get more info about where the sled is going)