Question

1) You have boasted to your friends that you can ride your bicycle at 30 kph (km per hour) over a 30 km race comprising two 15 km laps. However, when you finish the first lap, your coach tells you that your average speed so far is only 15 kph. How fast must you ride to bring your average speed up to 30 kph?

2) Jane's brother Andrew leaves home for school at 8:00 am. He walks at 3.6 kph. At 8:20 am Jane discovers that Andrew has left his homework at home. She decides to follow him on her bicycle and give him his homework, but she wants to be back home in time for an online test at 9 am. What is the minimum constant speed at which she needs to ride?

Jane must ride at least ______ kph. (Hint: At what time of day will they meet?)

3) A car accelerates with a constant acceleration of 1.2 m/s^2 along a long straight road. How long does it take the car to accelerate from 100 kph to 110 kph, and how far does it travel while doing so?

It takes ______ seconds to accelerate to 110 kph. While accelerating, the car travels _____ m.

Hint: watch your units and your significant figures. Because there is no other information, take the speeds as three significant figures.

4) A (field) hockey player is running north at a speed of 8m/s. A ball is coming directly towards her from the north at a speed of 18 m/s. She swings her stick forward, directly north, at a speed of 6 m/s measured in her own frame of reference. What is the speed of the ball with respect to the hockey stick?

Relative to the hockey stick, the ball is travelling at ____ m/s.

Answer 1

Solution

1) He cannot do it.

2) 7.2 kph

3) Time = 2.31 seconds, Distance= 67.4 meters

4) 32 m/s