Question

Motion please help

Answer 1

A pebble is thrown vertically upwards from a bridge with a initial velocity of 5m/s , if t strikes the water after 2 sec then find the height of the bridge over the water surface and the velocity with which it strikes the water

Answer 2

Find out how high the pebble will go before it begins to fall. (At maximum height v = 0). Then find out how long it takes to get there. Find out how high the pebble has gone from where it was thrown.

You know the total flight was 2 seconds. Subtract the time you got in the first part. The remaining time is how long it travels from it maximum height. If you know how long it takes to fall, calculate how far it falls (starting from rest) and its final vertical velocity. If you now know how far it fell, subtract from that how far ir first rose to get the height of the bridge.

Use your equations for constant accelerated motion in 2 dimensions to solve all parts of this problem, since this projectile is only moving up and down and not horizontally.

Answer 3

since it is assumed that the acceleration of gravity is pretty much a downward constant near the surface of the earth then we can approach this mathically as:

a(t) = -k , integrate to get velocity

v(t) = -kt + c1, such that v(0) defines the initial velocity. integrate again for position

s(t) = -kt^2/2 + c1 t + c2, such that s(0) gives us the initial height.