# Physics 9702 Doubts | Help Page 240

__Question 1115: [Work, Energy and Power]__
The kinetic energy of a vehicle of
mass 1000 kg is 4.5 × 10

^{5}J. It is stopped by applying a constant braking force of 6000 N.
What is its stopping distance?

A 37 m B 75 m C 150 m D 300 m

**Reference:**

*Past Exam Paper – November 2010 Paper 12 Q16*

__Solution 1115:__**Answer: B.**

The speed of the vehicle decreases
as it stops. The kinetic energy of the car is converted into work done to stop
it.

Work done in stopping vehicle =
braking force × stopping distance

4.5 × 10

^{5}= 6000 × s
Stopping distance, s = (4.5 × 10

^{5}) / 6000 = 75 m

__Question 1116: [Kinematics]__
A person, travelling on a motorway a
total distance of 200 km, travels the first 90 km at an average speed of 80 km
h

^{–1}.
Which average speed must be obtained
for the rest of the journey if the person is to reach the destination in a
total time of 2 hours 0 minutes?

A 110 km h

^{–1}B 120 km h^{–1}C 122 km h^{–1}D 126 km h^{–1}**Reference:**

*Past Exam Paper – November 2013 Paper 13 Q9*

__Solution 1116:__**Answer: D.**

Average speed = total distance /
total time

Time taken to travel first 90 km = 90
/ 80 = 1.125 h = 1 h 7.5 min

For the rest of the journey,

Distance that needs to be travelled
= 200 – 90 = 110 km

Time remaining = 2 h – 1.125 h =
0.875 h

Average speed = total distance /
total time = 110 / 0.875 = 126 km h

^{–1}

__Question 1117: [Vectors]__
A vector has magnitude R and
perpendicular components P and Q, as shown in the diagram.

Which row correctly describes the
perpendicular components?

vertical
component horizontal component

A Q
R sinθ

B R
cosθ P

C R
cosθ R
sinθ

D R
sinθ R cosθ

**Reference:**

*Past Exam Paper – June 2012 Paper 12 Q3*

__Solution 1117:__**Answer: D.**

From the diagram,

Vertical component Q = R sinθ

Horizontal component P = R cosθ

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