Physics Fundamentals
Physics Fundamentals
2nd Edition
ISBN: 9780971313453
Author: Vincent P. Coletta
Publisher: PHYSICS CURRICULUM+INSTRUCT.INC.
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Chapter 1, Problem 50P

(a)

To determine

The average speed of car.

(a)

Expert Solution
Check Mark

Answer to Problem 50P

The average speed of car is 60.0km/h .

Explanation of Solution

Given:

The average speed of car is 80.0km/h in first hour and 40.0km/h in second hour.

Formula used:

Average speed is defined as total distance travelled by an object in unit time interval.

Write the expression for average speed.

  v=dt ...... (1)

Here, d is the distance, t is the time and v is the average speed of object.

Rearrange the above expression in terms of d .

  d=vt ...... (2)

Calculation:

Substitute 80.0km/h for v and 1.00h in equation (2).

  d1=(80.0km/h)(1.00h)=80.0km

Substitute 40.0km/h for v and 1.00h in equation (2).

  d2=(40.0km/h)(1.00h)=40.0km

Calculate the total distance travelled by car.

  d=80.0km+40.0km=120km

Calculate the total time taken by car.

  t=1.00h+1.00h=2.00h

Substitute 120km for d and 2.00h in equation (1).

  v=120km2.00h=60.0km/h

Conclusion:

Thus, the average speed of car is 60.0km/h .

(b)

To determine

The average speed of the car.

(b)

Expert Solution
Check Mark

Answer to Problem 50P

The average speed of the car is 53.3km/h .

Explanation of Solution

Given:

The average speed in 1.00km is 80.0km/h and average speed in further 1.00km is 40.0km/h .

Formula used:

Rearrange the equation (II) in terms of t .

  t=dv ...... (3)

Calculation:

Substitute 1.00km for d and 80.0km/h for v in equation (3).

  t1=1.00km80.0km/h=1.0080.0h

Substitute 1.00km for d and 40.0km/h for v in equation (3).

  t2=1.00km40.0km/h=1.0040.0h

Calculate the total distance travelled by car.

  d=1.00km+1.00km=2.00km

Calculate the total time taken by car.

  t=1.0080.0h+1.0040.0h=3.0080.0h

Substitute 2.00km for d and 3.0080.0h for t in equation (1).

  v=2.00km( 3.00 80.0 h)=53.3km/h

Conclusion:

Thus, the average speed of the car is 53.3km/h .

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