Vertical Motion

Vertical motion:

1. When a body is dropped from a height under gravity and neglecting the resistive forces, then, initial velocity of the body (u) is zero. The acceleration of the body is a = g.

The velocity of the body at time t is v = gt [using v = u + at].

The distance travelled by the body for time t is h = [using ].

The velocity of the body when h height is travelled v = [using v2 = u2 + 2as].

2. When a body is thrown vertical upward with initial velocity u under gravitational acceleration g, then its final velocity is zero and it travels a maximum height H.

The velocity of the body at time t is v = u – gt [using v = u + at and a = – g].

The distance travelled by the body for time t is h = ut –  [using  and a = – g].

The velocity of the body when h height is travelled [using v2 = u2 + 2as and a = – g].

The maximum height travelled by the body is H =  [using v2 = u2 + 2as where v = 0 and a = – g].

Time of ascent and time of descent are same: A body is projected vertically upwards with velocity u and after time t it reaches the maximum height H before stop. Then using the equation v = u – gt we get, 0 = u – gt or, t = .

When the body is at height H then using the equation v2 = u2 – 2gH

We get, 0 = u2 – 2gH or, H = .

If the body takes time T to reach the ground from maximum height, then using the equation

Or, H = 0.T +

Or, =

Or, T = .

So, Time of ascent = time of descent.

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