12th grade forces and motion

Question 1

The distance between two masses is multiplied by 0.5. By what factor does the gravitational force between them change? (F = G m₁ m₂ ÷ r²; give 4 decimal places if needed)

Answer 

Question 2

A car goes round a bend twice as fast. How does the centripetal force needed change?

• A. it doubles
• B. it becomes four times larger
• C. it halves
• D. it stays the same

Question 3

A 800 kg object moves in a circle of radius 5 m at 15 m/s. What centripetal force is needed, in N? (F = m v² ÷ r)

Answer N

Question 4

A stone is thrown horizontally at 5 m/s from a cliff 19.6 m high. How far from the base of the cliff does it land, in m? (g = 9.8 m/s²; ignore air resistance)

Answer m

Question 5

A ball is kicked horizontally off a cliff 4.9 m high. Ignoring air resistance, how long does it take to reach the beach below, in s? (g = 9.8 m/s²; give 2 decimal places)

Answer s

Question 6

Calculate the gravitational field strength at the surface of Jupiter, in N/kg. Mass = 1.9 × 10²⁷ kg, radius = 6.99 × 10⁷ m, G = 6.67 × 10⁻¹¹ N m²/kg². (g = G M ÷ r²; give 1 decimal place)

Answer N/kg

Question 7

During a projectile's flight (no air resistance), what happens to its horizontal velocity?

• A. it reverses
• B. it increases
• C. it stays constant
• D. it decreases to zero

Question 8

Friction between the tyres and the road provides 3200 N of centripetal force for a 1000 kg car on a bend of radius 20 m. What is the car's speed, in m/s?

Answer m/s

Question 9

Gravitational force follows an "inverse square law". What does this mean?

• A. Distance has no effect
• B. Doubling the distance halves the force
• C. Doubling the distance doubles the force
• D. Doubling the distance makes the force one quarter as strong

Question 10

One of two masses is multiplied by 3 and the distance stays the same. By what factor does the gravitational force change? (F = G m₁ m₂ ÷ r²)

Answer 

Question 11

What provides the centripetal force for the Moon orbiting Earth?

• A. Earth's gravitational pull
• B. the Moon's engines
• C. friction with space
• D. magnetism

Question 12

A 0.5 kg object moves in a circle of radius 5 m at 5 m/s. What centripetal force is needed, in N? (F = m v² ÷ r)

Answer N

Question 13

A stone is thrown horizontally at 15 m/s from a cliff 19.6 m high. How far from the base of the cliff does it land, in m? (g = 9.8 m/s²; ignore air resistance)

Answer m

Question 14

A ball is kicked horizontally off a cliff 20 m high. Ignoring air resistance, how long does it take to reach the beach below, in s? (g = 9.8 m/s²; give 2 decimal places)

Answer s

Question 15

Calculate the gravitational field strength at the surface of Mars, in N/kg. Mass = 6.42 × 10²³ kg, radius = 3.39 × 10⁶ m, G = 6.67 × 10⁻¹¹ N m²/kg². (g = G M ÷ r²; give 1 decimal place)

Answer N/kg

Question 16

During a projectile's flight (no air resistance), what happens to its horizontal velocity?

• A. it decreases to zero
• B. it reverses
• C. it stays constant
• D. it increases