Please to help me with this physics HW. I have been working on the for a while.
ID: 1273559 • Letter: P
Question
Please to help me with this physics HW. I have been working on the for a while.
1. A woman drives a car from one city to another with different constant speeds along the trip. She drives at a speed of 85.0 km/h for 15.0 min, 60.0 km/h for 25.0 min,makes a stop for 45.0 min, then continues at 45.0 km/h for 30.0 min, at which point she reaches her destination.
(a) What is the total distance between her starting point and destination (in km)?
---km
(b) What is the average speed for the entire trip (in units of km/h)?
---- km/h
2. A race car completes a lap on a 1600 m long track with an average speed of 250 km/h. If the car's average speed on the first half of the track was 215 km/h, what was its average speed on the second half?
--- km/h
Explanation / Answer
a)
Total distance =sum of all speed * time
=(85*15/60) + (60*25/60) + (45*30/60)
= 68.75 km
b)
Total distance = 68.75 km
Total time= 15+25+45+30
=115 mins
= 115/60 hours
Average speed =total distance/total time
=68.75*60/115
=35.87 km/h
c)
Let the average speed for second half= x km/h
Total time= 0.8/215 + 0.8/x
= 3.72 + 0.8/x
Average speed =total distance/total time
or, total time= total distance/average speed
3.72 + 0.8/x = 1.6 /250
0.8/x=2.679*10^-3
x= 298.6
Ans: 298.6 km/h