Free Fall | Gravitation | Assessment | English | Grade 9

A 500 gm stone fell from the terrace of a building. What is the acceleration of the stone?

• 4.9 m/ s²

• 1.6 m/ s²

• 9.8 m/ s²

• 0 m/ s²

Answer explanation

The stone is in free fall, so the acceleration here is acceleration due to gravity. Therefore, a = 9.8 m/ s²

Tags

NGSS.HS-PS2-1

A rocket had travelled 2 × 10⁶ m from earth when it suddenly starts falling towards the earth. What will be gravity acting on the rocket when G= 6.7 ×10⁻¹¹ Nm²/kg², mass of the earth = 6 ×10²⁴ kg and Radius of earth = 6 × 10⁶ m?

• 10.05 m/ s²

• 9.8 m/ s²

• 6.25 m/ s²

• None of the above

Answer explanation

Here, the rocket is far from earth So, g = G M/d² = 6.7 ×10⁻¹¹ × 6 ×10²⁴/((2+6) × 10⁶)² = 6.25 m/s²

Tags

NGSS.HS-PS2-4

A water balloon is allowed to fall from a terrace and covers a distance of 50 m. What is the final velocity of the ballon?

• 40 m/s

• 20 m/s

• 60 m/s

• 100 m/s

Answer explanation

v²= u² + 2aS v² = 2 × 10 ×20 (g is taken as 10 m/s²) v = 20 m/s

Tags

NGSS.HS-PS2-4

Two balls are dropped from 2nd and 3rd floor of a building at the same time. What will be the ratio of the time covered taken by them, if the first ball is hollow? Take h1 and h2 as heights.

• h1/h2

• √h1/√h2

• h1²/h2²

• None of the above

Answer explanation

Let the distance covered by the balls be for the ball fall from 2nd floor = h1 for the ball fall from 3rd floor = h2 We know, acceleration due to gravity will remain the same in both the cases, a= 9.8 m/ s² S = ut + 1/2 gt² (here a is g) S = 1/2 gt² h1 = 1/2 gt'² h2 = 1/2 gt² Ratio of time,t'/t = √h1/√h2

Tags

NGSS.MS-PS2-2

NGSS.MS-PS2-4

Relief work was carried out both in equator and poles and equal amount of food packets were dropped from helicopters from the same height at the same time of 8:00 am. In which area will the food reach the people in less time?

• Food will reach early at the equator.

• Food will reach early at the poles.

• Food will reach at the same time in both equator and poles.

• None of the above

Answer explanation

The food will reach the people at poles in time as acceleration due to gravity is more at poles than in equator.

Tags

NGSS.HS-PS2-4

A ball is thrown upward with initial velocity of 40 m/s. What is the final velocity of the ball after 2 seconds?

• -40 m/s

• -30 m/s

• -20 m/s

• 0 m/s

Answer explanation

u = 40 m/s t = 2 seconds a = -10 m/ s²(as the ball is going against gravity) v = 40 + ( -10) × 2 = -20 m/s

Tags

NGSS.HS-PS2-1

Which of the following statement is true?

• acceleration due to gravity is same everywhere.

• In a free fall time taken is not affected by air resistance.

• acceleration due to gravity is always positive

• Gravity will be zero at the center of the earth.

Answer explanation

We know, g = G M / R² If an object is at center of earth, radius is 0. So, gravity will be zero.

Tags

NGSS.HS-PS2-4