Physics - ball dropped vs ball thrown downward

cubsarecute SG

1.If a ball is dropped from a height and another all is thrown vertically down from the same height, will the time they take to reach the ground the same? Why?

2.Two balls are dropped from different heights at the same time. As they accelerate toward the ground will their distance between them increase, decrease or stay the same?

Thanks!

Darkness_hacker99 SG

I'm not a physic student, but I can try to help you with this.

Both ball is dropped from the same height. Assuming the height is the same for both ball, I will call the ball that is freefall Ball A, and the ball that is thrown down Ball B.

They will not take the same time to reach the ground because Ball A is free falling, while Ball B is thrown to the ground with an initial force applied downwards.

Ball B will reach the ground first as it have a higher initial accerleration.

2) Assuming no downward force is applied to any balls, their distant will stay the same as both fall at the rate of 9.8s^2

Wait for the experts here to reply

alize SG

Agree with you there, but what is this 9.8ms-1 number we keep seeing?

Is it the maximum velocity of any object falling unassisted? Lots of objects can travel faster but is this their maximum velocity if simply dropped?

Also I think some falling objects will never attain 9.8ms-1.

CaiHongRainx SG

The 9.8m/s2 is acceleration due to gravity i think?
Sorry to hijack your post cubsarecute, for the 1), what happen if there is no air resistance (meaning in vacuum instead) ?

Okazaki SG

9.81 is simply the gravitational field strength NEAR Earth surface.You can’t apply 9.81 when it is not near Earth’s surface.You will learn it in H2 Physics under the topic of Gravitation.

In case you are wondering the formula of gravitational field strength of a mass m
g is,

g=GM/r^2

Where G is the Universal Constant,M is mass of body creating the field, r is the distance between bet. Both body Smile

Darkness_hacker99 SG

now we have someone that is talking real physics..

Piguchu SG

1: This is a good question , we shall name ball A as the one dropped from height , while ball B as the one thrown vertically down.

The answer to this question is that ball B would travel faster and reach the ground faster.

This is because there is an initial energy supplied to ball B as you throw it downwards , by principal of conservation of energy , the final kinetic energy of ball B ; at the instant before touching ground would be higher than ball A.

Note: We are under the assumption the total energy remains constant. In reality , we must consider energy lost as thermal energy or sound.

2: Stay the same. We presume the fact that both objects have the same air resistance or no air resistance is in play here.

PhdGuy SG

I'd prefer to be more precise in answering these two Physics questions. Sometimes, we can't trust our common sense. It's always better to argue from fundamental physics principles.

My thoughts on answers given by others:

In Question 1, while the Conservation of Mechanical Energy proves that ball B hits the ground with a higher speed, it still does not prove that the time taken for the overall motion is shorter. The extra step needed is that we need also to mention that the velocity is higher at every instant in time throughout the motion.

For Question 2, it's true that both balls are subject to the same acceleration of free fall. However, acceleration is rate of change of velocity, not displacement. Therefore, arguing that 'both are subject to same acceleration and therefore have same distance of separation' is not a complete explanation. One has to prove it precisely.