Questions: According To Newton's First Law Of Motion

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1. C
Why: according to Newton’s first law of motion, an object that is free from all outside forces travels at a constant velocity, covering equal distances in equal times along a straight-line path, C is true.
2. D
Why: not matter an object is still or is in motion, the object has inertia all the time. Inertia is a nature/property of any objects.
3. D
Why: the ship is moving at a constant speed, which is in a balanced status. For the athlete, it would be likely to do a long jump on ground. Since he uses the same strength every time he tries, the distance should be equal.
4. A
Why: before he jumps, he moves as the car does (with a same velocity); after he jumps off and lands, he still has the same velocity with the car, therefore, he could
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B
Why: inertia is the object’s resistance to changes in velocity and is related to the object’s mass. At first, those two balls are moving with car, so they has the same velocity. Since m1>m2, which means changing the velocity of the first ball is harder than the second’s does. After a while, the first ball will have a greater speed than the seconds, therefore, they will never meet each other.
6. D
Why: the person has the same velocity with the moving train, and because of the inertia, he fall back to the same location.
7. C
Why: net force is the sum of all the individual forces being exerted on an object. According to Newton’s Second Law, the direction of the acceleration is the same as the direction of the net force.
8. A
Why: one’s mass is fixed, while its weight varies at different location. Using the formula: weight = mass * acceleration due to gravity, we can get the object’s mass is 50kg. Then using the formula again, we get its weight on surface of the Moon is 80N
9. D
Why: when acceleration a = 0, the object does not change its motion status. The positive and negative signs of velocity refer to the direction and acceleration refers to the rate of velocity’s changes.
10.
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Other options could be think in the same way.
11. B
Why: Any change in your velocity is acceleration, including the change of speed or direction of travel.
12. B
Why: a constant velocity object has zero acceleration and using the formula: present velocity = initial velocity + acceleration * time, we can get a2 = (velocity-initial velocity)/ time = (4 - 0)/2 = 2 m/s2.
13. A
Why: using the formula present position = initial position + initial velocity * time + ½ acceleration * time2. Let the block’s original location be the original point, then present position will be 0 + 0*4 + ½ * 35 * 42 = 280. So the block moves 280 cm from the original point, which should – 65 to get the final answer 215 cm. It is easy to solve the question by graph a picture.
14. C
Why: according to Newton’s third law of motion, F1 and F2 are a pair of equal-but-opposite forces.
15. B
Why: F1 = (mb + mc) * a = 2ma, F3 = mc * a = ma. Therefore, F1 = 2F3
16. C
Why: when the weight lifer is going exert a force on his body, his body also exerts a equal but opposite force (according to Newton’s third law of

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