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Laws of Motion question

2003 · Shift 0 · Q179

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Laws of Motion
2003 · Shift 0 · Q179

Laws of Motion question

2003 · Shift 0 · Q179

JEE MainPhysicsLaws of MotionMCQ+4 / −1

A rocket with a lift-off mass

3.5 \times {10^4}\,\,kg

is blasted upwards with an initial acceleration of

10m/{s^2}.

Then the initial thrust of the blast is

A
$3.5 \times {10^5}N$
B
$7.0 \times {10^5}N$
C
$14.0 \times {10^5}N$
D
$1.75 \times {10^5}N$

View written solutionFree

Correct answer: B: $7.0 \TIMES 10^5\,N$

Given data

Mass of rocket:
$m = 3.5 \times 10^4\,\text{kg}$
Upward acceleration at lift-off:
$a = 10\,\text{m/s}^2$
Acceleration due to gravity:
$g \approx 10\,\text{m/s}^2$

Forces acting on the rocket

At lift-off, two main forces act:

Upward thrust: $T$
Downward weight: $mg$

Since the rocket accelerates upward with acceleration $a$ , applying Newton’s second law upward:

$T - mg = ma$

Calculate thrust

Rearranging,

$T = m(a+g)$

Substitute the values:

$T = 3.5 \times 10^4 (10+10)$

$T = 3.5 \times 10^4 \times 20$

$T = 7.0 \times 10^5\,\text{N}$

Match with the options

$7.0 \times 10^5\,\text{N}$ corresponds to Option B.

Check against stored answer

The stored correct answer is A, but the correct thrust from Newton’s second law is B.

So, the stored answer appears to be incorrect.

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