Help! Please?

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

I make it 20ms, but the options are:

4ms

8ms

40ms

80ms

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.

1 Answer
May 4, 2018

Please see the explanation below.

Explanation:

Here is what I think about this problem :

The horizontal velocity will remain constant.

ux=4ms1

Let the acceleration due to gravity g=9.8ms2

The vertical component of the velocity is =vy

After t=2s

vy(2s)=0+gt=9.82=19.6ms1

The velocity is

v(t)=v2x+v2y=19.62+42=20ms1

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

Good Luck!