(a). The power of the candy bar is,

The time taken to play on 800 kJ energy of the candy bar is,

where E is the energy.
Substituting the known values,

As 1 minute is equal to 60 seconds,
Thus,

Thus, the time taken to play tennis on the 800 kJ energy is 30.3 minutes.
(b). By doing the exercise, the process of digestion of food inside our body increases. Thus, the exercise does not helps us to burn the calories. But it helps us to diggest the heavy meal like candy bar easily.
The time taken to digest the canndy bar or to utilise its energy is large because it takes a lot of time to burn small amount of food and make it digest quickly.
Answer:
F = 1.6*10⁴ N
Explanation:
Given distance x = 0.15m, mass m = 1200kg, velocity v = 2m/s.
Unknown: force F
Force is given by Newton's law:
(1) 
The average force to stop an object from a velocity will be the same force necessary to accelerate an object from rest to the same velocity.
The distance for an object starting from rest for a constant acceleration is given by:
(2) 
The velocity for an object starting from rest for a constant acceleration:
(3) 
Using equation 2 and 3 to eliminate time t:
(4) 
Solving equation 4 for the acceleration a:
(5) 
Using equation1 to solve for the force F:
(6) 
Answer:
0.07756 m
Explanation:
Given mass of object =0.20 kg
spring constant = 120 n/m
maximum speed = 1.9 m/sec
We have to find the amplitude of the motion
We know that maximum speed of the object when it is in harmonic motion is given by
where A is amplitude and
is angular velocity
Angular velocity is given by
where k is spring constant and m is mass
So 

35%
5.43/15.6
This is how you calculate the percentage the answer is 35%