Answer:
(a) F = 239.575 N (b) t = 0.00649s or 6.49 ms
Explanation:
(a) By law of energy conservation, the bullet kinetic energy will be transferred to work done on stopping it from moving.
Formula for Kinetic Energy 
where m is bullet mass, v is the velocity
Formula for work 
where F is the average force and S is the distance travelled.
Substitute m = 4.2 g = 0.0042 kg, v = 370 m/s and S = 1.2 (m)
(b) If the force is constant, since the mass is constant and F = ma according to Newton's 2nd law, the acceleration on bullet is also constant
We also have 
At the time the bullet is coming to rest, 
Therefore, 
Answer:
43.75 miles must a person walk to utilize the energy in (“burn”) a pound of fat.
Explanation:
3,500 calories are present in 1 pound of the fat.
Thus, given that:
<u>4 calories are burnt in 1 minute of walking.</u>
So,
1 calories are burnt in 1/4 minute of walking.
Or,
<u>1 calories are burnt in 0.25 minute of walking.</u>
Thus,
<u>3500 calories are burnt in 0.25*3500 minutes of walking</u>
Minutes of walking needed to burn 3500 calories = 875 minutes.
Also, given that:
<u>20 minutes of walking covers 1 mile.</u>
<u>1 minute of walking covers 1/20 mile.</u>
So,
<u>875 minutes of walking covers (1/20)*875 mile.</u>
<u>43.75 miles must a person walk to utilize the energy in (“burn”) a pound of fat.</u>
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