Answer:
(a) -472.305 J
(b) 1 m
Explanation:
(a)
Change in mechanical energy equals change in kinetic energy
Kinetic energy is given by
Initial kinetic energy is 
Since he finally comes to rest, final kinetic energy is zero because the final velocity is zero
Change in kinetic energy is given by final kinetic energy- initial kinetic energy hence
0-472.305 J=-472.305 J
(b)
From fundamental kinematic equation

Where v and u are final and initial velocities respectively, a is acceleration, s is distance
Making s the subject we obtain
but a=\mu g hence

PE = mass * height * 9.81
PE = 142 * 25 * 9.81
PE = 34825.5 J
Answer:
20.179 x 10⁶ J /kg
Explanation:
The food after the reaction gives out heat which increases the temperature of water and air in the reaction chamber . The heat absorbed by water and air gives the estimate of energy content of the food.
Heat absorbed by water = mass x specific heat x rise in temperature
= 3 x 4.18 x 10³ x 3.2
= 40.128 x 10³ J
Heat absorbed by air = mass x specific heat x rise in temperature
0.1 x 3. 2 x .718 x 10³
= 0.23 x 10³
Total heat energy evolved
= 40.358 x 10³ J
This energy is evolved by 2 x 10⁻³ kg of food
energy content per kg of food
= 40.358 x 10³ / 2 x 10⁻³
= 20.179 x 10⁶ J /kg