Relative Motion

Observers using different ___________________ may measure different velocities for an object in motion

• frame of reference

• relatives of motion

• projectile motions

• constant velocity

What is the relative speed of the guy walking on the belt to the girl standing still on the walkway.

• 0 m/s

• 2 m/s

• 4 m/s

• 1 m/s

Answer explanation

The belt is moving at a rate of 2 m/s. The guys is walking on the belt moving at 2 m/s ON TOP OF the already moving 2 m/s. So these two speeds add together. 2+2 = 4 m/s

A boat heading north crosses a wide river with a velocity of 10.00 km/h relative to the water. The river has a uniform velocity of 5.00 km/h due east. What formula would you used to Determine the boat’s speed with respect to an observer on shore.

• subtraction (10-5)

• addition (10+5)

• division (10/5)

• Pythagorean Theorem (A² + B² = C²)

• Multiplication (10*5)

Answer explanation

Increasing the River Speed _____________ the time required for the boat to cross the river.

• increases

• decreases

• doesn't change

What is the relative velocity of the rabbit to the boat people?

(Reference West as negative, and East as Positive). W-E

• 10 m/s West

• 10 m/s East

• 0 m/s

• -10 m/s

Answer explanation

The boat people are approaching the bunny at 10 m/s west. That means that the bunny looks like it is approaching them from left to right at 10 m/s.

A boat heading north crosses a wide river with a velocity of 10.00 km/h relative to the water. The river has a uniform velocity of 5.00 km/h due east. Determine the boat’s speed with respect to an observer on shore.

• 11.18 km/hr

• 15 km/hr

• 5 km/hr

• 30 km/hr

Answer explanation

Use the Pythag. Theorem to solve for the velocity. the numbers in the example are NOT from the problem above.

Q What is the correct formula for relative velocity of a body A with respect to B?

• (a) v_R = v_B - v_A

• v_R = v_A - v_B

• v_R = v_B + v_A

• v_R = v_B x v_A

If two bodies are moving in opposite directions with non-zero velocities, which of the following statements is true?

• Relative velocity > Absolute velocity

• Relative velocity < Absolute velocity

• Relative velocity = Absolute velocity

• Relative velocity <= Absolute velocity

A point A is placed at a distance of 7 m from the origin, another point B is placed at a distance of 10 m from the origin. What is the relative position of B with respect to A?

• 4 m from A

• -3 m from A

• 3 m from A

• -7m from A

A jet airplane travelling at the speed of 450km/h ejects the burnt gases at the speed of 1200km/h relative to the jet airplane. find the speed of the burnt gases w.r.t a stationary observer on earth.

• 1750km/h

• 1200km/h

• 750km/h

• none of these