Basic Physics problems...can some1 check it?

Question

can someone check these questions for me? I

1. If a car moves with a constant velocity, it also moves with a constant speed because constant velocity means motion in a straight line in a constant speed.

2. The acceleration of a car that maintains a constant velocity of 100 km/h for 10s is

[Acceleration = change in velocity/time interval]
[Acceleration = 100km/h / 10s= 10km/hs]

The answer is 10km/hs

3. An object cannot reverse its direction of travel while maintaining a constant acceleration because we can change the velocity of an object by changing its direction; changes in velocity of an object will lead to changes in acceleration. Therefore, whenever the direction changes, both the velocity and the acceleration also change. For example, though a car is moving in a constant speed, its velocity changes when it u-turns.

4: If the net force acting on a sliding block is somehow tripled, by how much does the acceleration increase?

It’ll have three times as much acceleration

Answer 1

1. correct
2. incorrect, if the velocity is constant, then there is no acceleration.
3. Not sure about this one, what if the object is moving in a circle at a constant speed? the direction changes but the acceleration is constant.
4. correct

Answer 2

Unfair! That's 4 questions;-{ you could have gotten 20 points.

1. A car moves with constant velocity if it continues in a straight line.

2. Aceleration is change in velocity over time.
Moving at constant velocity, there is no change.

3. You mean, an object cannot maintain a constant velocity,
while changing it's direction, because that is a change in acceleration.

4. If the net force acts in the direction of travel, the velocity will change, we can say nothing about the acceleration.
That will depend on how long it is acting.

Answer 3

No, they are not all correct.

1 is correct.
2 is incorrect. As soon as you see 'constant velocity', this means that there velocity is not changing, which means there is no acceleration. If a=dV/dt, dV=0 because its not changing. so a =(0m/s)/10s = 0m/s^2

3. Incorrect. Best example is throwing straight up in the air. When you throw a ball up, there is a constant acceleration towards the earth of 9.8m/s^2, but the ball will still change direction from going up to coming down.

4. Correct, because F=ma. So if the Force triples and mass stays the same, acceleration must triple

Answer 4

Number 1 is correct

the answer to number 2:

acceleration is simply change in velocity. It doesn't involve change in time. Since the velocity is constant, the acceleration is 0 km/h^2

Number 3 is correct

Number 4

F= mass X distance / time (squared) so assuming the mass is unchanged, number 4 is also correct.

Three out of four isn't bad.

Answer 5

1. If the weight of the book is the action force then the reaction force is the table pushing up on the book. In turn, the table legs push down on the earth (the source of the weight of the book). Sounds a lot like your answer....... 2. a = f/m. The force (weight) must increase in proportion to the mass for a to be the same. Since we already know that f = mg, it is clear that f IS proportional to m, so the constancy of acceleration is verified. Multiple choice: 1. All three are correct. 2. c. includes both a & b, so it's the safest answer 3. I like both b & c, providing the tires mentioned are the driving tires. 4. b & c are both true

Answer 6

all of your four answers are correct.