physics problem princeton review

[synapse]

Advertisement - Members don't see this ad

Can someone explain this to me? I don't get it! This is a princeton review multiple choice physics problem

A projectile is launched horizontally from a raised platform. If air resistance is ignored, then as the projectile falls to the earth, the magnitude of the vertical component of the velocity of the projectile:

Answer: increases, while the horizontal component remains constant.

I understand why the horizontal component is constant.The part I don't get is why the vertical component of the velocity of the projectile increases as it falls to earth.

Can someone explain that part to me?

 

[nicholonious]

Can someone explain this to me? I don't get it! This is a princeton review multiple choice physics problem

A projectile is launched horizontally from a raised platform. If air resistance is ignored, then as the projectile falls to the earth, the magnitude of the vertical component of the velocity of the projectile:

Answer: increases, while the horizontal component remains constant.

I understand why the horizontal component is constant.The part I don't get is why the vertical component of the velocity of the projectile increases as it falls to earth.

Can someone explain that part to me?

Heres a shot in the dark. As it falls, gravitational force (9.8m/s^2) causes it to build acceleration as time elapses. So if you were to draw out velocity vectors for, say, every second, it would increase in magnitude, which would give you longer arrows as time passes.

If drawn, it should look like an upside down exponential curve (imagine half an arch, starting from top and progressing to bottom)

Hope this helps, I'm sure someone can explain it better, or better yet, correctly.

 

[BlackstarNYC]

Just think modified free fall

Vfy = Voy + at

As time progresses and the object moves downward, the y component of the velocity will increase.

Nicholonius, don't be so hard on yourself 😉 Your explanation is awesome.

 

[Parscope]

yep

Horozontally, It has an initial speed that stays constant.

Vertically, gravity is accelerating the object downward at a constant rate.

 

[tao]

uhhh....i thought it was cause the projectile was fired from a raised platform?
cause then, you'd have more time for gravity to act on it.

but i'm confused though, like...let's say the projectile wasn't fired from a raised platform, but was fired level to the ground....wouldn't the intial Vo of the object match the Vf right before the ball hits the ground? Like, i'm just assuming here, don't know if i'm talkin outta my ass or not?

 

[MattD]

Gravity is accelerating the projectile downward. Acceleration is the rate of CHANGE of velocity. So the vertical velocity is constantly CHANGING, i.e., getting larger (in the direction of the ground). There is no force to cause a horizontal acceleration (because we're neglecting air friction), so the rate of change of the horizontal velocity is 0. So horizontal velocity is constant and vertical velocity increases until it hits the ground. The path of the projectile will be parabolic, no matter what elevation or angle the projectile is fired at (ignoring changes in gravitational force due to changing altitudes... think small scale here).If the projectile is launched from a platform, it'll have more time to accelerate and will hit the ground with a higher velocity. If it's launched two inches above the ground, it'll just accelerate less, but it WILL still accelerate as it falls to the ground. make sense??

 

[stoleyerscrubz]

I'm thinking that you do not realize the vertical componet of the velocity starts at 0. It states that the projectile is launched horizontally so the angle is equal to 0.

cos 0 degrees=1
sin 0 degrees=0

A projectile is launched horizontally from a raised platform. If air resistance is ignored, then as the projectile falls to the earth, the magnitude of the vertical component of the velocity of the projectile:

Can someone explain that part to me?

 

[blankguy]

vertical component increases if we take the absolute value. If the projectile is shot horizontally. The velocity vector initially is all horizontal the vertical is 0. Nothing is acting on the projectile horizontally so it is constant however gravity is acting on it vertically so it is increasing(if we take the absolute value). The gravity is being added on a persecond basis. We add both components hence the projectile gives half an upside down parabola.