Projectile Motion Prac Question. (1 Viewer)

[chingyloke]

So basically the prac involved bouncing a golf ball on cement, calculating the time of flight and range and making further calculations from there.

Then i got the question:
Is the initial velocity of the ball (after the bounce) the same as the velocity at which it was thrown - and could we test this?

anyone shed some light for me?

 

[youngminii]

Was it thrown horizontally?
'Cause if so.. As you should know, a projectile keeps it's horizontal velocity the same throught it's flight
So if you threw it horizontally, it would have that horizontal velocity. Once it bounces, the initial velocity will consist of a horizontal AND vertical velocity, hence different from the velocity at which it was thrown

But if it's not horizontal, I'm stumped

 

[oh-em-gee]

So basically the prac involved bouncing a golf ball on cement, calculating the time of flight and range and making further calculations from there.

Then i got the question:
Is the initial velocity of the ball (after the bounce) the same as the velocity at which it was thrown - and could we test this?

anyone shed some light for me?

It would be difficult to test, but you could - you would need to measure the angle of depression from a horizontal, which would then allow you, using trigonometric ratios, to separate the velocity into its vertical and horizontal components. You'd have to do the same for the ball as it bounces.

Since we already know that horizontal and vertical components of a fall can be considered independent of each other, only the vertical component of the fall would be affected by gravity.

If you dropped it, by pushing it off a horizontal surface or otherwise, then there should be no change in the horizontal velocity. The vertical velocity will have changed, depending on the distance to fall.

You can work this out from the physics syllabus, page 42:

v_x² = u_x²

v_y² = u_y² + 2a_y²Δy

 

[chingyloke]

Was it thrown horizontally?
'Cause if so.. As you should know, a projectile keeps it's horizontal velocity the same throught it's flight
So if you threw it horizontally, it would have that horizontal velocity. Once it bounces, the initial velocity will consist of a horizontal AND vertical velocity, hence different from the velocity at which it was thrown

But if it's not horizontal, I'm stumped

it was thrown down into the ground at an arbitrary angle...

could i say it is unlikely but possible for the throwing and bounce velocities to be equivalent?




it is a silly question to begin with...

 

[darkchild69]

One thing i suppose you whould realise is that veloity is of course a vector.

Initially, the ball is travelling downwards (assuming you launched it at at a certain angle of depression)

After the bounce the ball is travelling upwards? Hence different velocity

Or is it assuming that it is at the instant with which the ball hits the ground and has no vertical velocity?

There will be losses of horizontal velocity due to friction and it not being a perfectly elastic collision.

That's a pretty poor question if the golf ball was initially launched at an undefined angle!