Student Question

1. Why is it harder to overcome the inertia of a bowling ball than a baseball?

A. because the bowling ball is larger

B. because the bowling ball has greater mass

C. because the baseball has less momentum

D. because the baseball has greater acceleration

2. In which situation will the friction between an object and the surface on which it is moving be increased?

A. The object is pushed over a longer distance.

B. The weight of the moving object is decreased

C. The object is pushed with greater force against the surface.

D. The surface on which the object is moving is made smoother.

4. From a complete stop, a car reaches a velocity of 280 km/s east in 7 seconds. What is the rate of acceleration?
A. 4 (km/s)/s
B. 7 (km/s)/s
C. 40 (km/s)/s
D. 70 (km/s)/s
 
5. On Earth, which forces tend to slow an object down?
A. friction and drag
B. drag and momentum
C. momentum and gravity
D. gravity and acceleration
 
6. Which formula is used to calculate acceleration?
A. time ÷ change in speed
B. time × change in speed
C. change in speed ÷ time
D. change in speed × time
 
 
 

 

Expert Answers

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6. Acceleration (instantaneous or average) is of course
C. change in speed ÷ time.

Therefore 4. (280 km/s) / (7 s) = 40 (km/s)/s, C.

1. It is not clear whether a balls considered at rest or moving at their usual speeds. In the first case "overcome the inertia" means "make a ball move with some speed" of course mass is a measure of inertia, and the answer is B.

But in the second case "overcome the inertia" probably means "stop a ball moving with usual speed" and the answer depends on momentum, which may be greater of any ball. So the answer is C if it is known that "is it harder to overcome the inertia of a bowling ball than a baseball".

2. The friction force depends on the properties of the surfaces and the pressure force (against the surface). So A is irrelevant, in the cases B and D the friction would decrease and in C it would increase. The answer is C.

5. Momentum and acceleration aren't forces, so the answer is A.

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