Question

I 1 A body is projected into air from the ground at an angle 90 to the horizontal. On reaching the highea point above the ground. a) its velocity is zero and acceleration is not zero b) its acceleration is zero and velocity is not zero c) both velocity and acceleration are not equal to zero d) both velocity and acceleration are equal to zero​

Answer 1

• (a) its velocity is zero & acceleration is not zero .

Explanation:

According to the Question

It is given that body is projected into air from the ground at an angle 90° to the horizontal.

On reaching the highea point above the ground.

Since the body reached at its maximum height so the velocity is zero ( final velocity) .

As we know when any body go upward or downward acceleration due to gravity is acting on that body .

Acceleration due to gravity is 9.8m/s².

So, at its maximum height acceleration due to gravity is acting in downward direction to pull it .

So, the acceleration is not zero .

So, the required option is

(a) its velocity is zero and acceleration is not zero .

Additional information !!

Formula to calculate maximum height attained by the body when it is projected with some Angle .

• $\bf \: H \: = \bf \frac{ {u}^{2}{sin} ^{2} \theta }{2g}$

Formula to calculate the horizontal range of the body

• $\bf \: R \: = \bf \: \frac{ {u}^{2}sin2 \theta }{g}$

Formula to calculate the time of flight of a body is

• $\bf \: T \: = \bf \frac{2u \: sin \theta}{g}$

Answer 2

UNDERSTANDING CONCEPT :-

• time taken to reach maximum height is equal to the time taken to reach to the earth as drag due to air is not considered while solving the projectile equations. Also, the horizontal acceleration is zero the only acceleration is in a vertical direction and which is the acceleration due to gravity. The acceleration for vertical motion will be acceleration due to gravity with a proper sign which is decided by the direction of motion of the body.

ANSWER:-

At the maximum height reached, the

• body comes to rest and thus its velocity becomes Zero while the acceleration due to gravity (g = 9.8 m/s²) acting. on it continues to act in downward direction and tries to bring the body back to the ground. Thus, at maximum height, the acceleration of the body is non-zero but its velocity is zero.

Hence, option A is the correct option.

ADDITIONAL INFORMATION :-

• sign of acceleration due to gravity is positive only if the motion is in the direction of acceleration due to gravity and the sign is negative if the motion is in the opposite direction of acceleration due to gravity.