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Motion in A Plane question

2021 · 27 Aug · Shift 2 · Q56
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  5. /2021 · 27 Aug · Shift 2 · Q56

Motion in A Plane question

2021 · 27 Aug · Shift 2 · Q56

JEE MainPhysicsMotion in A PlaneMCQ+4 / −1
A player kicks a football with an initial speed of 25 ms −-− 1 at an angle of 45 ∘^\circ∘ from the ground. What are the maximum height and the time taken by the football to reach at the highest point during motion ? (Take g = 10 ms −-− 2)
  1. A
    hmax = 10 m T = 2.5 s
  2. B
    hmax = 15.625 m T = 3.54 s
  3. C
    hmax = 15.625 m T = 1.77 s
  4. D
    hmax = 3.54 m T = 0.125 s
View written solutionFree

Correct answer: C

  1. Resolve the initial velocity into vertical component

Given: u=25 m/s,θ=45∘,g=10 m/s2u = 25\ \text{m/s}, \quad \theta = 45^\circ, \quad g = 10\ \text{m/s}^2u=25 m/s,θ=45∘,g=10 m/s2

The vertical component is uy=usin⁡θ=25sin⁡45∘=25⋅12=252 m/su_y = u\sin\theta = 25\sin45^\circ = 25\cdot \frac{1}{\sqrt{2}} = \frac{25}{\sqrt{2}}\ \text{m/s}uy​=usinθ=25sin45∘=25⋅2​1​=2​25​ m/s

  1. Time to reach the highest point

At the highest point, vertical velocity becomes zero. Using: vy=uy−gtv_y = u_y - gtvy​=uy​−gt

So, 0=252−10t0 = \frac{25}{\sqrt{2}} - 10t0=2​25​−10t t=25102=2.52≈1.77 st = \frac{25}{10\sqrt{2}} = \frac{2.5}{\sqrt{2}} \approx 1.77\ \text{s}t=102​25​=2​2.5​≈1.77 s

  1. Maximum height

Use the formula: H=uy22gH = \frac{u_y^2}{2g}H=2guy2​​

Substitute uy=252u_y = \frac{25}{\sqrt{2}}uy​=2​25​: H=(252)22⋅10H = \frac{\left(\frac{25}{\sqrt{2}}\right)^2}{2\cdot 10}H=2⋅10(2​25​)2​ H=625/220=62540=15.625 mH = \frac{625/2}{20} = \frac{625}{40} = 15.625\ \text{m}H=20625/2​=40625​=15.625 m

  1. Match with the options

We get:

  • Maximum height =15.625 m= 15.625\ \text{m}=15.625 m
  • Time to highest point =1.77 s= 1.77\ \text{s}=1.77 s

This matches Option C.

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