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Q14 P

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Physics For Scientists & Engineers
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Short Answer

Review: After a 0.300kg rubber ball is dropped from a height of 1.75 m, it bounces off a concrete floor and rebounds to a height of 1.50 m.

(a) Determine the magnitude and direction of the impulse delivered to the ball by the floor.

(b) Estimate the time the ball is in contact with the floor and use this estimate to calculate the average force the floor exerts on the ball.

(a) The magnitude and direction of the impulse delivered to the ball by the floor is3.38j^ kgm/s

.

(b) The average force the floor exerts on the ball is 7×102j^ N .

See the step by step solution

Step by Step Solution

Step 1: Concept

The impulse imparted to a particle by a net forcecan be calculated as the time integral of the force

I=titfFdt

where

I= Impulse delivered to object

F= Average friction force

Δt= Time interval in seconds.

The impulse-momentum theorem can help us to find the connection between the change in the horizontal momentum of the object to the horizontal force acting on it.

ΔPx=FxΔt

where

ΔPx= Change in the horizontal momentum

Fx= Average friction force

Δt= Time interval in seconds.

Step 2:Stating given data

The data given are listed below as

  • Mass of the ball, m=0.300 kg
  • The ball dropped from a height h1=1.75 m and rebounded to a height h2=1.50 m .

Step 3: Magnitude and direction of the impulse delivered to the ball by the floor

Part (a):

The impulse the floor exerts on the ball is equal to the change in momentum of the ball.

The magnitude and direction of the impulse delivered to the ball by the floor can be calculated as

ΔP=m(vfvi)=m(vfvi)j^

We know if the initial speed is zero, then the relationship between the final velocity and the height is

v=2gh

Then the final and initial velocity can be calculated as

vi=2gh1=2×9.8×1.75=5.8565.86 m/svf=2gh2=2×9.8×1.50=5.4225.42 m/s

Substitute the values in the above expression, we get

ΔP=(0.300 kg)[(5.42 m/s)(5.86 m/s)]j^=3.38j^  kgm/s

Thus, the magnitude and direction of the impulse delivered to the ball by the floor is 3.38j^ kgm/s

Step 4: Estimation of the time and finding the average force

Part (b):

Estimating the contact time interval to be0.05s .

So from the impulse-momentum theorem, we can calculate the average force as

F=ΔPΔt

Substitute the values in the above expression, we get

F=3.38 kgm/s0.05 sF=7×102j^ N

Thus, the average force the floor exerts on the ball is7×102j^ N .

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