Remember your physics.

Classical Mechanics Level 3

A ball is thrown upward. It's initial vertical component of velocity is 30m/s, and it's initial horizontal velocity is 10m/s. Neglecting air resistance, what are the velocities of the two components added up 5 seconds later.


The answer is 30.

Robert Fritz by Robert Fritz , 20, USA

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

3 solutions

Jasper Jamir
Mar 1, 2014

Actually the answer is WRONG.

--- Since it is already going downwards, the current direction of the motion is opposite the initial direction. By convention, it should be negative of the initial. Thus, the vertical component of the velocity should be [-20] but not [20]. So the sum should be [-10].

4 Helpful 0 Interesting 0 Brilliant 0 Confused

True , but most people aren't that technical. Plus, since it's still technically moving with a velocity, it's not really negative. You would probably be a good business man.

Robert Fritz - 7 years, 3 months ago

Yeah. The answer to this question is the sum of the speeds of the two component. Velocity, by definition depends on direction, which in this case is negative in the answer since the question establishes a convention with the upward direction being positive.

Tristan Goodman - 2 years, 5 months ago

I really did get confused - for it took me a while in finding the correct answer, for I kept on answering [-10]. Haha :) But velocity is a vector quantity thus the negative sign is a must. The negative sign doesn't imply that there is "no "/ "negative" velocity, it just simply implies that it's direction is opposite to the positive ones.

Jasper Jamir - 7 years, 1 month ago
Alex Li
Feb 23, 2015

Please clarify that you are using 10 for g and not 9.8

0 Helpful 0 Interesting 0 Brilliant 0 Confused

v=u-g t i.e. 0=30-10 t implies t=3 when the ball reaches topmost points. We need to calculate the same after 5 seconds so vertical velocity component at t'=5-3=2 sec i.e. v'=0+10*2=20 As air resistance assumed zero horizontal velocity component doesn't change =10 So Vertical + Horizontal velocity=20+10=30 (g=10m/sec^2 assumed)

0 Helpful 0 Interesting 0 Brilliant 0 Confused

Thx for posting a solution

Robert Fritz - 7 years, 3 months ago

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...