Suppose an object undergoes a change in velocity from +1m/s to 4m/s. Is its velocity becoming more positive or less positive than it was before? What direction (s) is the object moving? Is the acceleration positive or negative? Explain your response.
Are the velocity and acceleration in the same direction during the time interval of the change in velocity? Explain.
Hint 1
Find out whether difference between the initial and final velociyt is positive or negative. Us the formula V-U+at to determine whether the acceleration is positive or negative.
Answer 1
Initial velocity u = 1 m/s. Final velocity v = 4 m/s. Velocity is becoming more positive as
v - u = 4 - 1 = 3 m/s is positive. Object is moving in the positive direction. Acceleration is positive as the velocity is increasing.
Yes, the velocity and acceleration are in the same direction during the time interval of the change in velocity as only then the velocity can increase. We can see this from the first equation of motion:
v = u + at
v is greater than u only if a is positive that is in the same direction as v.
Question 2
Suppose an object undergoes a change in velocity from –4m/s to 1m/s.
Is its velocity becoming more positive or less positive than it was before?
What direction (s) is the object moving? Is the acceleration positive or negative?
Are the velocity and acceleration in the same direction during the time interval of the change in velocity? Explain
Hint 2
Initially the object is moving in the negative direction. When the force is applied,
it decelerates and continues to move in the negative direction. Proceed with this line of thought to reach the answer.
Answer 2
Velocity is becoming more positive
u = - 4 m/s v = 1 m/s
Change in velocity = v - u = 1 - (-4) = 5 m/s which is positive.
Initially the object is moving in the negative direction. When the force is applied,
it decelerates and continues to move in the negative direction.
Eventually its velocity becomes zero and then it starts to move in the positive direction.
Thus acceleration is positive.
Initially the velocity and acceleration are in opposite directions till velocity becomes zero.
Then acceleration and velocity are in the same direction This is because first the body decelerate,
its velocity going from -4m/s to 0 m/s, then it changes direction, and body accelerates from 0 to 1 m/s
Question 3
Suppose an object is turning around so that it undergoes a change in velocity from –2m/s to +2m/s.
Is its velocity becoming more positive or less positive than it was before? What direction (s) is the object moving?
Is the acceleration positive or negative? Are the velocity and acceleration in the same direction
during the time interval of the change in velocity? Explain.
Hint 3
Object is moving in the negative direction initially. It decelerates, stops and begins to move in the positive direction.
Answer 3
Velocity is becoming more positive.
u = -2 m/s and v = 2 m/s
v - u = change in velocity = 2 - (-2) = 4 m/s
Object is moving in the negative direction initially. It decelerates, stops and begins to move in the positive direction.
The acceleration is positive.
Initially velocity is negative, acceleration is positive, that is why the body decelerates. When the velocity of object becomes zero, the velocity and acceleration start acting in the same direction and the body's speed increases from 0 to 2 m/s.
Question 4
An object is turning around so that it undergoes a change in velocity from +1 m/s to –1m/s.
Is its velocity more positive or less positive than it was before? What direction (s) is the object moving?
Is it undergoing acceleration while it is turning around? Is the acceleration positive or negative?
Are the velocity and acceleration in the same direction during the time interval of the change in velocity?
Hint 4
The object is initially moving in the positive direction. It decelerates stops and starts moving in the negative direction.
First it undergoes deceleration till speed becomes zero then it accelerates.
Answer 4
u = 1 m/s , v = - 1 m/s
Change in velocity = v-u = -1 -1 = -2 m/s
Velocity is less positive than it was before.
The object is initially moving in the positive direction. It decelerates stops and starts moving in the negative direction.
First it undergoes deceleration till speed becomes zero then it accelerates.
Acceleration is negative.
Velocity and acceleration are in the opposite direction when body is moving towards the positive direction.
After it stops and changes direction, velocity and acceleration are in same direction that is both acting along the negative direction
Question 5
A ball is thrown down vertically with an initial speed of 20.5 m/s from a height of 58.8 m.
What will be its speed just before it strikes the ground?