Work done in each beat= 1.5 J
Time taken, t = 1 min = 60 s
Power, P = 2 W = 2 Js^-1
Total work done = P x t = 2 Js^-1 x 60 s = 120 J
Number of times heart beats per minute=Total work done/Work done in each beat = 120/1.5 = 80 times.

Work done by the heart per beat = 1J
Work done by the heart in 72 beats, W = 1 x 72 = 72 J
Time taken, t = 1 min = 60 s.
Power P = W/t = 72J/60 s = 1.2W

Here W = 50 J, t = 5 s
Power P = W/t = 50 J/5 s = 10 W

K.E. of mass m=P.E. lost by mass m = mgh
K.E. of mass 2m=P.E. lost by mass 2m
= 2m x g x 2h = 4mgh.
Hence, mass 2m will have a greater kinetic energy on reaching the ground.

As the body falls, its potential energy gradually changes into kinetic energy.On reaching the ground, the whole of its potential energy gets converted into kinetic energy.But when the balls strikes the ground, the kinetic energy is converted into sound, light and heat.When the ball strikes the ground, the kinetic energy is converted into sound, light and heat.

All these objects possess energies of the following forms:
(i) potential
(ii) both kinetic and potential
(iii) both kinetic and potential
(iv) potential
(v) potential
(vi) potential
(vii) potential

m = 100 g = 1/10 kg, K.E = 20 J
K.E = 1/2 mv²
20 = 1/2 x 1/10 x v²
v² = 400 or v = 20 m/s
Momentum, p = mv = 1/10 x 20 = 2 kg m/s.

m = 10 g, p = 100 g cm/s
p = mv
v = p/m = 100/10 cm/s = 1/10 m/s
K.E.= 1/2mv² = 1/2 x 10/1000 x (1/10)²J = 5 x 10^-5J

K.E.= 1/2mv².If mass is increased four times, the velocity must be reduced to half to maintain the same kinetic energy.
(K.E.= 1/2mv² = 1/2 x 4m(v/2)² = 1/2mv²)

(i) K.E. of a body is directly proportional to its mass.
\(K.E.\alpha m\)
(ii) K.E. of a body is directly proportional to the square of its velocity.
\(K.E.\alpha { v }^{ 2 }\)

W = 48.4J, s = 40 cm = 0,40 m
Force F = W/s = 48.4J/0.40 = 121 N

Here m = 10 kg, W = 490J, s = ?
W = F s = mg x s
s = W/mg = 490/10 x 9.8 = 5m

Here F = 150N, s = 50m
Work done, W = F s = 150 N x 50 m = 7500 J

Here, Force(F) = 140N, Displacement (s) = 15m
Work done, W = Fs = 140 N x 15 m = 2100 J

Zero, because displacement of the rock is zero.