Question

Help! Please?

A projectile is thrown from the top of a building with initial horizontal velocity `4 m/s`. The building is 45m high. What is the velocity of the projectile after 2 seconds.

I make it `20 m/s`, but the options are:

`4 m/s`

`8 m/s`

`40 m/s`

`80 m/s`

I keep recalculating according to how you are supposed to solve these, but still get the same answer. I don't no what else to do.

Thanks.

Answer 1

Please see the explanation below.

Explanation:

Here is what I think about this problem :

The horizontal velocity will remain constant.

`u_x=4ms^-1`

Let the acceleration due to gravity `g=9.8ms^-2`

The vertical component of the velocity is `=v_y`

After `t=2s`

`v_y(2s)=0+ g t =9.8*2= 19.6ms^-1`

The velocity is

`v(t)=sqrt(v_x^2+ v_y^2)=sqrt(19.6^2+4^2)=20ms^-1`

I get the same answer as you. There is a mistake either in the question or in the options.

Good Luck!