Question

A ball is thrown horizontally from a point 100 m above the ground with a speed of 20 m/s. Find a. the time it takes to reach the ground, b. the horiontal distance it travels before reaching the ground, c. the velocity (direction and magnitude) with which it strikes the ground.

Answer 1

Correct Answer - B
It is case of projectile fired horizontally from a height h. `g 9.8 m/s^2`
a. time taken to reach the ground
` t= sqrt((2h/g))
sqrt((2xx100)/9.8)=4.51 sec
Horizontal range
x= ut= 20xx4.5=90m
c. horizontal velocity remains constant throgh out the motion. At A, v_x = 20 m/s
v_y= u+at=0+9.8xx4.5
= 44.1 m/s` Resultant velcity
`v_r(sqrt(44.1)^2+20^2)
tan beta = v_y/v_x= 44.1/20=2.205
rarr beta= tan^-1 (2.205)=66^0` The ball strikes teh ground with a velocity of 48.42 m/s at an agle `66^0` with horizontal.