Question

(vi). A metal ball of mass 2kg is allowed to fall freely from rest from a height of 10 m above the ground [19 =10 m/s2]

(A)The potential energy possessed by the ball when it is initially at rest.
(a) 200 J
(b) 300 J
(c) 100 J
(d) 50 J

(B) The kinetic energy of the ball just after it hits the ground
(a) 200 J
(b) 300 J
(c) 100 J
(d) 50 J

(C) The mechanical energy of the ball after it hits the ground and comes to rest is
(a) kinetic energy changes into potential energy
(b) potential energy changes to kinetic energy
(c) mechanical energy converts into heat energy.
(d) mechanical energy converts into heat and sound energy both. ​

Answer 1

Answer:

(A)The potential energy possessed by the ball when it is initially at rest - 200J

(B) The kinetic energy of the ball just after it hits the ground - 200 J

(C) The mechanical energy of the ball after it hits the ground and comes to rest is - mechanical energy is converted into both heat and sound energy.

Explanation:

Mass of the metal ball = 2 Kg

Since the ball is under free fall, initial velocity, u = 0 m/s

Height from the ground before falling, h = 10 m

(A) The potential energy possessed by the ball when it is initially at rest is:

     P = mgh

        = 2 × 10 × 10

 ∴ P = 200 J

(B) The kinetic energy of the ball just after it hits the ground  is also 200 J. Because At the ground level potential energy is fully converted into kinetic energy.

(C) The mechanical energy of the ball after it hits the ground and comes to rest is converted into both heat and sound energy. Because energy can neither be created nor be destroyed. It is transformed from one form to another.

Answer 2

Answer:

A (a)

B. (a)

C. (d)

Explanation:

A.

When ball is at rest it will only have Potential Energy that is,

P.E=mgh

m= 2 kg;h= 10m

P.E=2×10×10=200J

This is the total energy as K.E is zero when the ball is at maximum height that is when it is at 10 m. Hence when the ball reaches the ground P.E becomes zero because of zero height.At this point,the total energy is equal to the K.E that is K.E=200J.

B.

Kinetic energy of the ball just before hitting the ground = Initial potential energy= mgh = 2×10×10 = 200J

C.

(d) mechanical energy converts into heat and sound energy both.