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For the one-dimensional motion, describe by x = t - \sin t

a)\; x(t)>0 for \; all\; t>0

b) v(t)>0 for\; all\; t>0

c) a(t)>0\; for \; all\; t>0

d) v(t) lies\; between\; 0 \; and \; 2

Answers (1)

The correct answer is the option:

a)\; x(t)>0 for \; all\; t>0

d) v(t) lies\; between\; 0 \; and \; 2

Explanation: Now, x = t -\sin t

We know that v=\frac{dx}{dt}

                           =1-\cos \; t

Now, a=\frac{dv}{dt}

             =\frac{d(1-\cos \; t)}{dt}

             =+\sin\; t

 vmax will be,

             V_{max}=1-(-1)

            = 1+1 = 2

. vmin will be,

v_{min} = 1-1

            =0

Thus, it is clear that v lies between 0 to 2 and option (d) is verified.

Now, x = t -\sin t

Thus, sin t lies between 1 and -1 for all t > 0.

Thus, x will always be positive and option (a) is verified.

Now, v = 1 -\cos \; t

v= 0, when \; t = 0

v= 1, when\; t = \frac{\pi }{2}

v=2, when t = \pi

& v= 0, when\; t = 2\pi .

Hereby opt (b) is discarded.

Now, a = \sin \; \; t

a = 0, when\; t = 0

a = 1, when \; t = \frac{\pi }{2}

a = 0, when\; t = \pi

& a = 1, when\; t = 2\pi .

Thus, acceleration can be negative as well, and hence opt (c) is also discarded here.

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