Question

a stone is thrown vertically upward with a speed of 20 m per second how high it will go

Answer 1

Initial speed(u)=20 m/s

v^2=u^2+2as

At maximum height,speed=0
so v=0.

0=(20)^2+2(-g)(H)

2gH=400
H=200/g
g=9.8 m/s^2
H=200/9.8 metres.

:-)

Answer 2

the initial velocity is given as 20m/s, i.e., u=20m/s, the final velocity that the ball can achieve at the maximum height is 0m/s, hence, v=0m/s. Since the only first that cause the acceleration is gravity, a is taken as g where g is acceleration due to gravity, and had a value of 9.81m/s2. But for simplicity, we can take the value of a to be 10m/s2, so a=10m/s2. Now, we need to find, what's s and t.

Note: Since the ball is thrown upwards, which is against the force of gravity (gravity always acts downwards), we need take the value of a (in this case, g) as −10m/s2.

Using the first equation,

v=u+at

0=20−10t

10t=20

t=2

Using the third equation,

v2=u2+2as

02=202+2×(−10)×s

20s=400

s=20

Hence, the ball will travel for 2 seconds and complete a distance of 20 metres upwards.