Super Sleigh On Frictionless Ice

A sleigh rests on a smooth, frictionless sheet of ice. It is then pushed with an accleration of 2 meters per second squared. Assuming that is continues in motion indefinitely, find its velocity in m/s after traveling 9 meters.


The answer is 6.

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16 solutions

Mayank Shreshtha
Dec 20, 2013

Since , initially the sledge is at rest , therefore

u = 0 \boxed{u = 0}

also, we know that :

v 2 u 2 = 2 a s \boxed{v^{2} - u^{2} = 2as}

where s = distance travelled and v = final velocity.

So, just plug in the values : u = 0 , s = 9 m , and a = 2 m/ s 2 s^{2}

we get v = 2 a s \sqrt{2as} = 6 m/s

If it is pushed than the force is not continously acting over it during its motion. As the contact is released no accelaration will be there. So how we are taking a constant accelaration on it.

Nitish Dubey - 7 years, 4 months ago

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there is no resistance since the surface is frictionless. hence it will have constant acceleration.

Malhar Punde - 7 years, 3 months ago

Nice!!

Wilson Widyadhana - 7 years, 4 months ago

good

Pervez Karim - 7 years, 3 months ago

exercises here are hard, i ve never study these knowlegde before

Mai Pham - 7 years, 2 months ago
Desmond Kan
Dec 22, 2013

We use the equation of motion v^2 = u^2 + 2as where v is its resultant velocity, u is its initial velocity, a is the acceleration and s is the displacement with respect to starting point. Clearly u = 0, a = 2, s = 9. Substituting these values into the equation, we get v = 6.

J Mar
Jan 18, 2014

Much like any other motion problem, let us begin by finding the equation of motion that governs this particular situation. Unsurprisingly, Newton´s second law is used:

Σ \Sigma F \overrightarrow{F} = d d t \frac{\mathrm d}{\mathrm d t} P \overrightarrow{P}

where P \overrightarrow{P} is the linear momentum vector and F \overrightarrow{F} the force vector. Seeing as we may assume that the mass of the sled remains constant, we can simplify the above vector equation to the form:

Σ \Sigma F \overrightarrow{F} = m d d t m\frac{\mathrm d}{\mathrm d t} V \overrightarrow{V}

since the derivative of the mass with respect to time is zero and recalling that:

P \overrightarrow{P} = m V m\overrightarrow{V}

With the push, the equation of motion must account for a net force acting on the sled:

2 m 2m = m d d t m\frac{\mathrm d}{\mathrm d t} V V

We now have a scalar equation since the respective force vector and velocity vector components were set equal to each other. Of course an inertial frame of reference is used to describe these vectors. Solving this simple differential equation gives:

\int 2 d t 2dt = \int d V dV

V ( t ) V(t) = 2 t + k 2t+k

Assuming the sled is at rest initially:

V ( t ) V(t) = 2 t 2t

Now we know how the velocity of the sled varies with time. The next step is to determine how its position varies with time. To do this, we integrate the above equation again with respect to time knowing that the derivative of position with time is velocity we have:

2 t 2t = d d t \frac{\mathrm d}{\mathrm d t} X X

\int 2 t d t 2tdt = \int d X dX

X ( t ) X(t) = t 2 + k t^2+k

Considering the position at zero seconds to be zero:

X ( t ) X(t) = t 2 t^2

We now know how the sled´s position varies with time. Knowing that the sled moved 9 9 meters, we can solve for the time taken for this to happen:

t 2 t^2 = 9 9 \Rightarrow t = 3 s e c o n d s t = 3 seconds

Finally, using this information in our velocity function we obtain the solution:

V ( t = 3 ) V(t=3) = 2 ( 3 ) 2(3) = 6 m / s \boxed{6 m/s}

Aravind Raj
Mar 2, 2014

By using newton's eqn of motion,

v^2-u^2=2as v^2=229 = 36 therefore, v=6 m/s.

nic

Surfaraz Ali - 7 years, 2 months ago

v^2-u^2=2 a s; where u=0,s=9,a=2 therefore, by equating v get v=6ms^-1

Koyal Suman
Mar 22, 2014

by using laws of kinematics.. v2=u2+2as..u=0,a=2,s=9.....hence,v2=2 9 2=36, that implies v=6

Dimas Nugroho
Feb 8, 2014

as we know, V^2 =v^2+2 a x d V = Velocity after traveling 9 meters; v = the first velocity; a = the acceleration; d = is the distance.

V^2 = 0 + 2 x 2 x 9 V^2 = 36 V = 6 m/s

Lucky Khan
Jan 27, 2014

Using third equ: of motion.... 2aS = vf^2 - vi^2 vi = 0, vf^2 = 2 2 9 = 36 vf = 6 m/s

Shiemka Juson
Jan 8, 2014

Given: a=2 m/s^2 d=9 m Vi=0 m/s

Required: Vf

Solution: 2ad = Vf^2 - Vi^2

                    2(2 m/s^2)(9 m) = Vf^2 - (0 m/s)^2

                    Vf^2 = 36 m^2/s^2

                    Vf = 6 m/s     ]ans.

the given acceleration is 2 m/s^2. As the question says that the sleigh rests on a smooth frictionless sheet of ice, therefore u = 0. The distance travelled is 9m. Therefore, by using newton's eqn of motion,

v^2-u^2=2as v^2=2 2 9 = 36 therefore, v=6 m/s.

v^2= 2.2.9

toshali mohapatra - 7 years, 5 months ago
Puja Shree
Dec 24, 2013

u=0 v=? a=2m/s sq s=9m

by third eq. of motion . v(sq) - u(sq) = 2as by substituting the values , we get v= 6 , answer

Vt squared = Vo squared + 2.a.x Vt squared = 0 + 2 . 2 . 9 Vt squared = 36 Vt = 36 rooted Vt = 6

Eleon Amorim
Dec 23, 2013

v2=v02+2ad v2=0+2.2.9 entao: v=6m/s

Budi Utomo
Dec 23, 2013

s = Vo.t + 1/2 . a . t^2 = 0 + 1/2 . a . t^2 = 1/2 . a . t^2 ---> 9 = 1/2 . 2 . t^2 ----> t = 3. So, Vt = Vo + at ---> Vt = 0 + 2 . 3 [m/s] = 6 m/s. Answer : 6

Prasun Biswas
Dec 22, 2013

Let the initial and final velocity after travelling 9 m be 'u' and 'v' resp,. Let the distance travelled be s = 9 =9 m. Also, let the acceleration of the sleigh be a = 2 =2 m/ s 2 s^{2} . Since, sleigh starts from rest, we have u = 0 =0 .

We here use the motion equation v 2 = u 2 + 2 a s v^{2}=u^{2}+2as to solve this problem.

So, v 2 = u 2 + 2 a s v 2 = 0 2 + 2 × 2 × 9 v 2 = 0 + 36 v 2 = 36 v = 6 [ v^{2}=u^{2}+2as \implies v^{2}=0^{2}+2\times 2\times 9 \implies v^{2}=0+36 \implies v^{2}=36 \implies v=6 [ Neglecting ( 6 ) (-6) as velocity cannot be negative. ] ]

So, we finally get v = 6 v=\boxed{6}

Nice solution I was ' nt able to do ! thank you !

Devesh Rai - 7 years, 5 months ago
Carl Denton
Dec 22, 2013

We use the equation v 2 = v 0 2 + 2 a Δ x v^2=v_0^2+2a\Delta x . Plugging in, we have v 2 = 2 ( 2 ) ( 9 ) = 36 v^2 = 2(2)(9) = 36 , and v = ± 6 v=\pm 6 . Assuming the direction of push to be positive, we reject the negative solution and have the answer as x = 6 x=6 .

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