First slide

Vertical projection from ground

Question

A juggler keeps on moving four balls in the air throws the balls in regular interval of time. When one ball leaves his hand (speed = 20 m/s), the positions of other balls will be (take g = 10 m/s²)

Easy

A

10m,20m,10m
B

15m,20m,15m
C

5 m, 15 m, 20 m
D

5 m, 10 m, 20 m

Solution

The time taken by the ball to reach its maximum height is given by
v=u-gt or 0 =20 -10 x t
$∴$ t=2s
The positions of different balls are shown in figure
The maximum distance travelled in given by
$h = ut - \frac{1}{2} {gt}^{2}$
or $h = 20 \times 2 - \frac{1}{2} \times 10 \times (2)^{2} = 20 m$
Distance travelled by first ball
$\begin{array}{l} h_{1} = \frac{1}{2} {gt}^{2} = \frac{1}{2} \times 10 \times (1)^{2} = 5 m \\ h_{2} = \frac{1}{2} {gt}^{2} = \frac{1}{2} \times 10 \times (2)^{2} = 20 m \end{array}$
The distances from ground a.re
15m,20m,15m

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