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Motion in A Plane question

2025 · 22 Jan · Shift 1 · Q74
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  5. /2025 · 22 Jan · Shift 1 · Q74

Motion in A Plane question

2025 · 22 Jan · Shift 1 · Q74

JEE MainPhysicsMotion in A PlaneNumerical+4 / −1
A particle is projected at an angle of 30∘30^{\circ}30∘ from horizontal at a speed of 60 m/s60 \mathrm{~m} / \mathrm{s}60 m/s. The height traversed by the particle in the first second is h0\mathrm{h}_0h0​ and height traversed in the last second, before it reaches the maximum height, is h1h_1h1​. The ratio h0:h1h_0: h_1h0​:h1​ is ‾\underline{\hspace{2cm}}​. [Take, g=10 m/s2\mathrm{g}=10 \mathrm{~m} / \mathrm{s}^2g=10 m/s2 ]
Numerical answer
View written solutionFree

Correct answer: 5

  1. Resolve the initial velocity vertically

The particle is projected with speed u=60 m/su=60\,\text{m/s}u=60m/s at angle 30∘30^\circ30∘.

So the vertical component is uy=usin⁡30∘=60⋅12=30 m/s.u_y=u\sin 30^\circ=60\cdot \frac{1}{2}=30\,\text{m/s}.uy​=usin30∘=60⋅21​=30m/s.

  1. Height traversed in the first second, h0h_0h0​

Vertical displacement in time ttt is y=uyt−12gt2.y=u_y t-\frac{1}{2}gt^2.y=uy​t−21​gt2.

For the first second, t=1t=1t=1 s: h0=30(1)−12(10)(1)2=30−5=25 m.h_0=30(1)-\frac{1}{2}(10)(1)^2=30-5=25\,\text{m}.h0​=30(1)−21​(10)(1)2=30−5=25m.

  1. Time to reach maximum height

At maximum height, vertical velocity becomes zero: 0=uy−gt0=u_y-gt0=uy​−gt 0=30−10t0=30-10t0=30−10t t=3 s.t=3\,\text{s}.t=3s.

So the particle reaches maximum height after 333 seconds.

  1. Height traversed in the last second before reaching maximum height, h1h_1h1​

The last second before reaching the top is from t=2t=2t=2 s to t=3t=3t=3 s.

Compute heights at these times: y(2)=30(2)−12(10)(2)2=60−20=40 my(2)=30(2)-\frac{1}{2}(10)(2)^2=60-20=40\,\text{m}y(2)=30(2)−21​(10)(2)2=60−20=40m y(3)=30(3)−12(10)(3)2=90−45=45 my(3)=30(3)-\frac{1}{2}(10)(3)^2=90-45=45\,\text{m}y(3)=30(3)−21​(10)(3)2=90−45=45m

Hence, h1=y(3)−y(2)=45−40=5 m.h_1=y(3)-y(2)=45-40=5\,\text{m}.h1​=y(3)−y(2)=45−40=5m.

  1. Find the ratio

h0:h1=25:5=5:1.h_0:h_1=25:5=5:1.h0​:h1​=25:5=5:1.

Since the integer asked is the ratio value, h0h1=5.\frac{h_0}{h_1}=5.h1​h0​​=5.

Therefore, the required answer is 5.

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