Centripetal Acceleration & Relative Velocity

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

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

Two cars X and Y move on adjacent roads in opposite directions. If velocity of car X and Y is 80 km/hr and 60 km/hr respectively, then what will be the relative velocity of car X w.r.t. Y?

• 70 km/hr

• 140 km/hr

• 20 km/hr

• -140 km/hr

Two trains 120m and 80m in length are running in opposite directions with velocities 42km/h and 30km/h. In what time they will completely cross each other?

• 2s

• 10s

• 12s

• none of these

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

A train is moving at a velocity of 15 m/s East. A passenger at the back of a train throws a baseball with a speed of 15 m/s West. What is the velocity of the baseball relative to the ground? (In other words: how fast does a person on the ground see the ball move?)

• 30 m/s East

• 30 m/s west

• 0m/s

• 60m/s west

A dog and a cat are about to fight, running towards each other, both at 12 m/s. What are their velocities relative to each other?

• 12 m/s

• 24 m/s

• 0 m/s

• 6 m/s

Assume that there is a current of 2.0 m/s directed south in the river, and that the ferry’s velocity of 7.0 m/s north is relative to the water. What is the ferry’s velocity relative to the shore? What is your velocity relative to the shore?

• 5.0 m/s N

• 5.0 m/s S

• 9.0 m/s N

• 9.0 m/s S

Object a moves relative to object b, and object b moves relative to object c. Which equation shows the correct way to find the relative velocity of object a to object c?

• va/c + va/b = vb/c

• va/b + vb/c = va/c

• va/c + vb/c = va/b

• vb/c + vc/b = va/c

When both an object and the reference frame it moves in move in the same direction, how do you find the velocity of the object relative to the ground?

• Add the squares of the velocities.

• Average the velocities.

• Add the velocities

• Subtract the velocities.