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Question -

A truck starts from rest and acceleratesuniformly at 2.0 m sтАУ2. At┬аt┬а= 10 s, a stone isdropped by a person standing on the top of the truck (6 m high from theground). What are the (a) velocity, and (b) acceleration of the stone at┬аt┬а=11 s? (Neglect air resistance.)



Answer -

Answer:┬а(a)┬а22.36 m/s, at anangle of 26.57┬░ with the motion of the truck

(b)┬а10 m/s2

(a)┬аInitial velocity of the truck,┬аu┬а=0

Acceleration,┬аa┬а= 2 m/s2

Time,┬аt┬а= 10 s

Asper the first equation of motion, final velocity is given as:

v = u + at

=0 + 2 ├Ч 10 = 20 m/s

Thefinal velocity of the truck and hence, of the stone is 20 m/s.

At┬аt┬а= 11 s, the horizontalcomponent (vx) of velocity, in the absence of air resistance, remainsunchanged, i.e.,

vx┬а= 20 m/s

The vertical component (vy) ofvelocity of the stone is given by the first equation of motion as:

vy┬а= u + ay╬┤t

Where, ╬┤t┬а= 11 тАУ 10 = 1 s and┬аay┬а=g = 10 m/s2

тИ┤vy┬а= 0 + 10 ├Ч 1 = 10m/s

The resultant velocity (v) of thestone is given as:

Let┬а╬╕┬аbe the angle made bythe resultant velocity with the horizontal component of velocity,┬аvx

=26.57┬░

(b)┬аWhen the stone is droppedfrom the truck, the horizontal force acting on it becomes zero. However, thestone continues to move under the influence of gravity. Hence, the accelerationof the stone is 10 m/s2┬аand it acts vertically downward.

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