A 10 kg ball is dropped from a height of 10m. Find (a) the initial potential energy of the ball. (b) the kinetic energy just before it reaches the ground, and (c ) the speed just before it reaches the ground.

Answer

B

Explanation

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.