Physics problems: kinematics

Part 5


Problem 41.

A motor scooter travels east at a speed of 13 m/s. The driver then reverses direction and heads west at 17 m/s.  What was the change in velocity of the scooter?



Problem 42.

A bicycle travels 3.2 km due east in 0.1 h, the 3.2 km at 15.0 degrees east of north in 0.21 h, and finally another 3.2km due east in 0.1 h to reach its destination. The time lost in turning is negligible. What is the average velocity for the entire trip?



Problem 43.

A swimmer dived off a cliff with a running horizontal leap. What must his minimum speed be just as he leaves the top of the cliff so that he will miss the ledge at the bottom which is 2 m wide and 9 m below the top of the cliff?



Problem 44.

A ferries wheel with radius 20 m which rotates counterclockwise, is just starting up. At a given moment, a passenger on the rim of the wheel and passing through the lowest point of his circular motion is moving at 3.00m/s and in gaining speed at a rate of .

Find the magnitude of the passenger's acceleration at the instant.



Problem 45.

In an action film hero is supposed to throw a grenade from his car, which is going 90.km/h, to his enemy's car, which is going 110 km/h. The enemy's car is 15.8 m in front of the hero's when he lets go of the grenade. If the hero throws the grenade so its initial velocity relative to him is at an angle of 45(degree) above the horizontal, what should the magnitude of the initial velocity be? The cars are both traveling in the same direction on a level road. Ignore air resistance.

Find the magnitude of the velocity both relative to the hero and relative to the earth.





Problem 46.

A flowerpot falls from a windowsill 25.0 m above the sidewalk.      

(a) how fast is the flowerpot moving when it strikes the ground?

(b) how much time does a passerby on the sidewalk below have to move out of the
        way before the flowerpot hits the ground?



Problem 47.

A tennis ball is thrown vertically upward with an initial velocity of +8.0 m/s.

(a) what will the ball\'s speed be when it returns to its starting point?

(b) how long will the ball take to reach its starting point?



Problem 48.

Problem 4.14 of Serway & Jewett: A firefighter, a distance d from a burning building,
directs a stream of water from a fire hose at angle above the horizontal. If the initial
speed of the stream is , at what height h does the water strike the building?



Problem 49.

If it takes a player 3 seconds to run from the batter's box to the first base at an average speed of 6.5 m/s, what is the distance she covers in that time?



Problem 50.

A car goes down a certain road at an average speed of 40 km/h and returns along the same road at an average speed of 60 km/h.  Calculate the average speed for the round trip.






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