A particle starts from the origin at t = 0 s with a velocity of 10.0 \$\hat{j}\$ m/s and moves in the x-y plane with a constant acceleration of \$\left ( 8.0\hat{i}\,+\,2.0 \hat{j}\right )\$ m/\$s^2\$.(a) At what time is the x- coordinate of the particle 16 m? What is the y-coordinate of the particle at that time?(b)What is the speed of the particle at the time ?

Given:The initial velocity of particle is \$\vec u = 10 \hat j m/s\$The acceleration of the particle is \$\vec a = 8 \hat i +2 \hat j\$(a)The position of the particle at any instant is given by:\$\vec s = \vec ut + \dfrac{1}{2}{\vec at}^2\$\$x \hat i + y \hat j = 4t^2 \hat i + (10t + t^2)\hat j\$Comparing the X and Y component of the position:\$x=4t^2\$\$x=16 \implies t=2 s\$\$y=10t+t^2\$At t=2, \$y=24 m\$(b)The speed of the particle at any instant is given by:\$\displaystyle {\vec {v}=\vec {u}+\vec a t}\$\$ {\vec {v} = 10\hat j +({8\hat i+2\hat j})2} \$\${\vec{v} = 14\hat j +16\hat i}\$\$|\vec{v}| = \sqrt {14^2+16^2} = 21.26 m/s\$

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>>Class 11
>>Physics
>>Motion in a Straight Line
>>Uniformly Accelerated Motion
>> $Velocity - Time Relation in Uniform Acce...$

Velocity - Time Relation in Uniform Acceleration Motion

Q: A ball is thrown vertically upwards with a velocity of \${20 ms^{-1}}\$ from the top of a multi storey building.The height of the point where the ball is thrown 25 m from the ground.How long will it be before the ball hits the ground ? Take \${g= 10 ms^{-2}}\$.

Time to reach maximum height can be obtained from \$v=u+at\$\$0=20+(-10)t\$\$t=2 s\$\$s=ut+0.5at^2=20(2)+0.5(-10)(2)^2= 20 m\$Thus, total distance for maximum height is 45 m\$s=ut+0.5at^2\$\$45=0+0.5(10)(t')^2\$\$t'=3 s\$Total time= 3+2= 5s

Q: A ball is dropped from a high rise platform at \$t=0\$ starting from rest. After 6 seconds another ball is thrown downwards from the same platform with a speed \$v\$. The two balls meet at \$t=18s\$. What is the value of \$v\$? (Take \$g=10m/{s}^{2}\$)

The distance traveled by the first ball in 18s is \$h=\dfrac{1}{2}gt^2=\dfrac{1}{2}\times 10\times (18)^2=1620 m\$Now to meet second ball has to same distance in\$(18-6)=12s\$So for second ball,\$h=vt+\dfrac{1}{2}gt^2\$\$1620=v\times 12+ \dfrac{1}{2}\times 10\times (12)^2\$\$v=\dfrac{1620-720}{12}=75 m/s\$

Q: A particle experiences constant acceleration for \$20\$ seconds after starting from rest. If it travels a distance \${ s }_{ 1 }\$ in the first \$10\$ seconds and distance \${ s }_{ 2 }\$ in the next 10 seconds, then

Let \$a\$ be the constant acceleration of the particle. Then\$s=ut+\displaystyle\dfrac { 1 }{ 2 } a{ t }\displaystyle^{ 2 }\$ or \${ s }_{ 1 }=0+\displaystyle\dfrac { 1 }{ 2 } \times a\times { \left( 10 \right) }\displaystyle^{ 2 }=50a\$and \${ s }_{ 2 }=\left[ 0+\displaystyle\dfrac { 1 }{ 2 } a{ \left( 20 \right) }^{ 2 } \right] -50a=150a\$\$\therefore \quad { s }_{ 2 }=3{ s }_{ 1 }\$ Alternatively:Let \$a\$ be constant acceleration and \$s=ut+\displaystyle\dfrac { 1 }{ 2 } a{ t }\displaystyle^{ 2 }\$, then \${ s }_{ 1 }=0+\displaystyle\dfrac { 1 }{ 2 } \times a\times 100=50a\$ Velocity after 10 sec. is \$v=0+10a\$ So, \${ s }_{ 2 }=10a\times 10+\displaystyle\dfrac { 1 }{ 2 } a\times 100=150a\Rightarrow { s }_{ 2 }=3{ s }_{ 1 }\$ Let \$a\$ be constant acceleration, using \$s=ut+\displaystyle\dfrac { 1 }{ 2 } a{ t }\displaystyle^{ 2 }\$ so distance coreved in first 10 seconds \${ s }_{ 1 }=0+\displaystyle\dfrac { 1 }{ 2 } \times a\times 100=50a\$ Velocity after 10 sec. is \$v=0+10a\$ So, distance covered in next 10 seconds \${ s }_{ 2 }=10a\times 10+\displaystyle\dfrac { 1 }{ 2 } a\times 100=150a\Rightarrow { s }_{ 2 }=3{ s }_{ 1 }\$

Q: A particle moves in a straight line with a constant acceleration. It changes its velocity from \$ 10 ms^{-1} \ to \ 20 ms^{-1}\$ while passing through a distance \$135m\$ in \$t\$ second. The value of t is

\$u=10m/s,v=20m/s,x=130m\$\$a=\cfrac{v-u}{t}=\cfrac{20-10}{t}=\cfrac{10}{t}\$\$s=ut+\cfrac{1}{2}at^2\\\implies 135 =10t+\cfrac{1}{2}\cfrac{10}{t}t^2\\\implies t=9s\$

Q: If a car at rest accelerates uniformly to a speed of 144 km\$h^{-1}\$ in 20 s, then it covers a distance of:

Given\$u=0\$\$v=144kmph=144\times\frac{5}{18}=40 m/s\$\$t=20sec\$We know,\$v=u+at\$\$40=a\times20\$\$a=2m/s^2\$Now,\$s=ut+\frac{1}{2}at^2\$\$s=\frac{1}{2}at^2=\frac{1}{2}\times2\times20^2=400m\$

Q: A body \$A\$ starts from rest with an acceleration \$a_1\$. After \$2\$ seconds, another body \$B\$ starts from rest with an acceleration \$a_2\$. If they travel equal distances in the \$5^{th}\$ second, after the start of \$A\$, then the ratio \$a_1\$ : \$a_2\$ is equal to

Initial speed \$u = 0\$Distance covered in nth second after starting from rest \$S = \dfrac{1}{2}(2n-1)\$For A : \$n = 5\$So, \$S_A = \dfrac{a_1}{2}(2\times 5-1) = \dfrac{9}{2}a_1\$For B : \$n = 3\$So, \$S_B = \dfrac{a_2}{2}(2\times 3-1) = \dfrac{5}{2}a_2\$But \$S_A=S_B\$Or \$\dfrac{9}{2}a_1 = \dfrac{5}{2}a_2\$\$\implies \ a_1:a_2 = 5:9\$

Q: A ball is dropped on the floor from a height of 10 m. It rebounds to a height of 2.5 m.If the ball is in contact with the floor for 0.01 sec, then average acceleration during contact is

Let u be the velocity with which the ball hits the ground, then\$\displaystyle { u }^{ 2 }=2gh\$\$\displaystyle =2\times 9.8\times 10=196\$\$\displaystyle \therefore \quad u=14 m/sec\$If v be the velocity with which it rebounds, then\$\displaystyle { v }^{ 2 }=2\times 9.8\times 2.5=49\$\$\displaystyle \Rightarrow v=7m/sec\$\$\displaystyle \therefore \quad \Delta v=\left( v-u \right) \$\$\displaystyle =\left( 7m/sec \right) -\left( -14m/sec \right) \$\$\displaystyle =21m/sec\$\$\displaystyle \therefore \quad a=\frac { \Delta v }{ \Delta t } =\frac { 21 }{ 0.01 } \$\$\displaystyle =2100{ m }/{ { s }^{ 2 } }\$

Q: A particle starts from rest, accelerates at \$2\ ms^{-2}\$ for \$10\ s\$ and then goes for constant speed for \$30\ s\$ and then deceleration at \$4\ ms^{-2}\$ till stops after next. What is the distance travelled by it?

Displacement in first, \$10\,\sec \$ \${{s}_{1}}=\dfrac{1}{2}{{a}_{1}}{{t}_{1}}^{2}=\dfrac{1}{2}\times 2\times {{10}^{2}}=100\,m\$ Speed achieve in first \$10\,\sec \$ \${{v}_{1}}={{u}_{1}}+{{a}_{1}}{{t}_{1}}=0+2\times 10=20\,m/s\$ Displacement in \$30\,\sec \$, acceleration is zero. \${{s}_{2}}={{v}_{1}}{{t}_{2}}=20\times 30=600\,m\$ Displacement in last due to deacceleration, \${{a}_{3}}=-4\,m/{{s}^{2}}\$ \$ {{v}^{2}}-{{v}_{1}}^{2}=2as \$ \$ {{s}_{3}}=\dfrac{0-{{20}^{2}}}{2\times (-4)}=50\,m \$ Net displacement \${{S}_{total}}={{s}_{1}}+{{s}_{2}}+{{s}_{3}}=100+600+50=750\,m\$ Total displacement is \$750\,m\$

Q: A car accelerates from rest at constant rate of \$2 m/s^2\$ for some time. Then its retards at a constant rate of \$4 m/s^2\$ and comes to rest. if it remains in motion for \$3\$ seconds, then the maximum speed attained by the car is:-

Let \$v, t_1,t_2\$ be the maximum velocity attained, time for which car accelerated and the time for which car retarded respectively\$\Rightarrow t_1=(v-u)/a=(v-0)/2=v/2\$\$\Rightarrow t_2=(v-u)/a=(0-v)/(-4)=v/4\$Now it is given that, \$\Rightarrow t_1+t_2=3\$\$\Rightarrow v/2+v/4=3\$\$\Rightarrow v=4m/s\$Hence correct answer is option \$C \$

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A ball is thrown vertically upwards with a velocity of 20ms−1 from the top of a multi storey building.The height of the point where the ball is thrown 25 m from the ground.How long will it be before the ball hits the ground ? Take g=10ms−2.

A ball is dropped from a high rise platform at t=0 starting from rest. After 6 seconds another ball is thrown downwards from the same platform with a speed v. The two balls meet at t=18s. What is the value of v? (Take g=10m/s2)

A particle experiences constant acceleration for 20 seconds after starting from rest. If it travels a distance s1​ in the first 10 seconds and distance s2​ in the next 10 seconds, then

A particle moves in a straight line with a constant acceleration. It changes its velocity from 10ms−1 to 20ms−1 while passing through a distance 135m in t second. The value of t is

If a car at rest accelerates uniformly to a speed of 144 kmh−1 in 20 s, then it covers a distance of:

A body A starts from rest with an acceleration a1​. After 2 seconds, another body B starts from rest with an acceleration a2​. If they travel equal distances in the 5th second, after the start of A, then the ratio a1​ : a2​ is equal to

A ball is dropped on the floor from a height of 10 m. It rebounds to a height of 2.5 m.If the ball is in contact with the floor for 0.01 sec, then average acceleration during contact is

A particle starts from rest, accelerates at 2 ms−2 for 10 s and then goes for constant speed for 30 s and then deceleration at 4 ms−2 till stops after next. What is the distance travelled by it?

A car accelerates from rest at constant rate of 2m/s2 for some time. Then its retards at a constant rate of 4m/s2 and comes to rest. if it remains in motion for 3 seconds, then the maximum speed attained by the car is:-

A ball is thrown vertically upwards with a velocity of $20 m s^{- 1}$ from the top of a multi storey building.The height of the point where the ball is thrown 25 m from the ground.How long will it be before the ball hits the ground ? Take $g = 10 m s^{- 2}$ .

A ball is dropped from a high rise platform at $t = 0$ starting from rest. After 6 seconds another ball is thrown downwards from the same platform with a speed $v$ . The two balls meet at $t = 18 s$ . What is the value of $v$ ? (Take $g = 10 m / s^{2}$ )

A particle experiences constant acceleration for $20$ seconds after starting from rest. If it travels a distance $s_{1}$ in the first $10$ seconds and distance $s_{2}$ in the next 10 seconds, then

A particle moves in a straight line with a constant acceleration. It changes its velocity from $10 m s^{- 1} t o 20 m s^{- 1}$ while passing through a distance $135 m$ in $t$ second. The value of t is

If a car at rest accelerates uniformly to a speed of 144 km $h^{- 1}$ in 20 s, then it covers a distance of:

A body $A$ starts from rest with an acceleration $a_{1}$ . After $2$ seconds, another body $B$ starts from rest with an acceleration $a_{2}$ . If they travel equal distances in the $5^{t h}$ second, after the start of $A$ , then the ratio $a_{1}$ : $a_{2}$ is equal to

A particle starts from rest, accelerates at $2 m s^{- 2}$ for $10 s$ and then goes for constant speed for $30 s$ and then deceleration at $4 m s^{- 2}$ till stops after next. What is the distance travelled by it?

A car accelerates from rest at constant rate of $2 m / s^{2}$ for some time. Then its retards at a constant rate of $4 m / s^{2}$ and comes to rest. if it remains in motion for $3$ seconds, then the maximum speed attained by the car is:-