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Form a lift moving upwards with a unifor...

Form a lift moving upwards with a uniform acceleration `a=2 m s^(-2), man throus a ball vertically upwards with a velcoity `v=`12 m s^(-1)` relative to the lift. The ball comes back to the man after a time `t`. Find the value of `t` in seconds.

Text Solution

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The correct Answer is:
2
Taking upward direction as positive, let us workin the frome of lift. Acceleration of ball relative to lift `=(g+a)` downwards, so `a_(real) =- (g+a)`, initial velocity: `u_(rel) =v`, final velcity : `v_(rel) =v`, as the ball will reach the man with same speed w.r.t. lift Apply `v_(rel) =u_(rel)+ a_(rel)t rArr - v+ (g-a)t rArr t =2 s` .
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Knowledge Check

  • A ball thrown vertically upwards with an initial velocity of 1.4 m//s. The total displcement of the ball is

    A
    `22.4cm`
    B
    zero
    C
    `44.8m`
    D
    `33.6m`

  • An elevator car (lift) is moving upward with uniform acceleration of 2 m//s^(2) . At the instant, when its velocity is 2 m/s upwards a ball thrown upward from its floor. The ball strikes back the floor 2s after its projection. Find the velocity of projection of the ball relative to the lift.

    A
    `10 m//s uarr`
    B
    `10 m//s darr`
    C
    `12 m//s uarr`
    D
    `12 m//s darr`

  • A man in a lift ascending with an upward acceleration a throws a ball vertically upwards with a velocity v with respect to himself and catches it after t_1 seconds. After wards when the lift is descending with the same acceleration a acting downwards the man again throws the ball vertically upwards with the same velocity with respect to him and catches it after t_2 seconds?

    A
    The acceleration of the ball w.r.t. ground is g when it is in air
    B
    the velocity v of the ball relative to the ligt is `(g(t_1+t_2))/(t_1+t_2)`
    C
    the acceleration `a` of the lift is `(g(t_2-t_1))/(t_1+t_2)`
    D
    The velocity `v` of the ball relative to the man is `(gt_1t_2)/((t_1+t_2))`